Flash Activity Research Articles

Self-reported sleep in postmenopausal women.

We aimed to find how self-reported sleep (measured by the St. Mary's Hospital Sleep Questionnaire) in postmenopausal women having hot flash activity was related to objective sleep (actigraphy), psychological and somatic symptoms [Women's Health Questionnaire (WHQ)], and cognitive test performance (computerized tests). A secondary aim was to find if self-reported sleep showed expected correlations with hyperarousal (Hyperarousal Scale). Drug trial baseline data from 88 healthy, postmenopausal women were retrospectively analyzed. Multivariate regression was used to adjust for confounder variables and test whether differences in self-reported sleep measures were systematically associated with differences in objective sleep, WHQ symptom measures, or cognitive test performance scores. Increased self-report scores for low sleep quality were associated with an increased risk of WHQ symptoms and reduced cognitive test performance. Self-reported sleep measures showed little correlation with their analogous objective measures. Self-reported low sleep quality proved most closely associated with the WHQ symptoms of tiredness, clumsiness, and difficulty concentrating. Women whose self-reported sleep-onset latency times were longer than the median overestimated their objective sleep onset time by 30 min, whereas the other women underestimated theirs by 15 min (P < 0.0001). Women whose self-reported total sleep was longer or shorter than the median, respectively, underestimated objective sleep times by 9 and 71 min (P < 0.0001). High hyperarousal scores were associated with underestimations of objective sleep. Self-reports of lower sleep quality were associated with increased WHQ psychological and somatic symptom measures and decreased cognitive test performance more than with differences in objective sleep. Self-reported trouble sleeping may signal problems independent from objectively low sleep quality, such as subjective distress or diminished cognitive function.

Cloud‐to‐ground lightning activity in hail‐bearing storms

The cloud‐to‐ground lightning flash (CG) produced by several apparent hailstorms are analyzed in different locations of southern Europe. The hail detection is performed via four different analysis techniques: radar reflectivity factor estimation, radar echo shape analysis, polarimetric hydrometeor identification, and reflectivity difference between radars with different wavelengths. The CG parameters considered are the flash rate and density, the flash polarity, the multiplicity, and the peak current. Some of the observed storms exhibit hail‐bearing cell features, while others exhibit heavy precipitation rates without any apparent hail production. One of the hailstorms can be classified as severe because reported hailstorm diameters reach 39 mm. The CG lightning characteristics of both types of storms are compared. The CG rates corresponding to all hail‐bearing storms are singularly lower than those of rain‐only storms, typically by a factor 5. So, the CG rate of the hail‐bearing storms considered does not exceed 2 min−1 while it can reach about 12 min−1 for heavy rain‐bearing storms. Moreover, some of them can produce especially high positive CG proportions associated with negative CGs with low values of peak current and multiplicity. This last observation suggests that the negative charge available for CG flashes is weak within the cloud when positive CG flashes are dominant. In order to interpret the low CG rates observed in the case of hail‐bearing storms several interpretations are discussed, but it would be necessary to know the intracloud flash activity in such cases of storms in order to enrich the discussion.

The Stopped-flow Method and Chemical Intermediates in Enzyme Reactions – A Personal Essay

My perspective does not deal directly with photosynthesis research. However, the methods evolved have played an important role in several areas of biochemistry and biophysics including photosynthesis. Improvements of rapid reaction methods, based upon the pioneering studies of Hamilton Hartridge and F.J.W. Roughton, and Glenn Millikan, required a detailed study of the hydraulics of small-bore tubes and jet mixers, taking into account, that economy of reactants was demanded by the sparcity of enzyme preparations in the 1930s. This Personal perspective recites the steps taken to minimize the volumes expended in rapid flow studies, together with the improvements in electronic technology of rapid and sensitive spectrophotometry of labile intermediates in enzyme reactions. Of the methods studied, continuous, accelerated and stopped flow, the latter was designed for the highest fluid economy and subsequently proved to be of wide use for studying biochemical kinetics. Advances in fast spectrophotometry of dilute solutions led to great improvements in Millikan's dual-wavelength system, both in speed of recording and decreases of background noise level, largely due to electronic stabilization of light sources and sensitive amplifiers. The application of these technologies to studies of hemoglobin, myoglobin and heme enzymes was, more recently, followed by studies of suspensions of organelles, cells, and tissues not only in vivo but also at low temperatures with cryoprotectants, leading to the use of flash activation in carbon monoxide inhibited heme enzymes. Laser technology allowed photosynthetic systems to be studied at cryotemperatures, leading to the development of electron tunneling theories for biological reactions (not discussed in this paper). All in all, the many fundamental developments of electronics, optics and hydraulics indicate how technology can respond effectively to the needs of biology in general, and photobiology in particular.

Lightning activities on the Tibetan Plateau as observed by the lightning imaging sensor

Lightning flash activities on the Tibetan Plateau are investigated using observations from the lightning imaging sensor. About 95% of the flashes are found to occur during May to September with a single peak in the summer from June to August. There is substantial lightning activity in May on the plateau, especially on the southern and eastern plateau. The diurnal variation of the lightning activity shows a prominent peak from 1500 to 1700 LT for most of the plateau with earlier activity on the eastern and southern plateau and a delay on the western, northern, and central plateau. Few lightning flashes are observed between 0000 and 1000 LT. The highest flash density is found in the grassland central plateau with a value of 4.5 flashes km−2 yr−1, while the minimum is found in the semiarid western plateau with a value of 1.5 flashes km−2 yr−1. The optical radiance of flashes fits a lognormal distribution. More energetic flashes are found on the mountainous eastern and northern plateau, and weaker flashes are found on the wet southern and semiarid western plateau. A nonlinear relationship between lightning activity and monthly averaged convective available potential energy (CAPE) is found. The flash number per CAPE on the Tibetan Plateau is much larger than it is for other regions with prominent lightning activity (but low altitude).

The Modified Q-cycle Explains the Apparent Mismatch between the Kinetics of Reduction of Cytochromes c1 and bH in the bc1 Complex

Crystallographic structures of the bc1 complex from different sources have provided evidence that a movement of the Rieske iron-sulfur protein (ISP) extrinsic domain is essential for catalysis. This dynamic feature has opened up the question of what limits electron transfer, and several authors have suggested that movement of the ISP head, or gating of such movement, is rate-limiting. Measurements of the kinetics of cytochromes and of the electrochromic shift of carotenoids, following flash activation through the reaction center in chromatophore membranes from Rhodobacter sphaeroides, have allowed us to demonstrate that: (i) ubiquinol oxidation at the Qo-site of the bc1 complex has the same rate in the absence or presence of antimycin bound at the Qi-site, and is the reaction limiting turnover. (ii) Activation energies for transient processes to which movement of the ISP must contribute are much lower than that of the rate-limiting step. (iii) Comparison of experimental data with a simple mathematical model demonstrates that the kinetics of reduction of cytochromes c1 and bH are fully explained by the modified Q-cycle. (iv) All rates for processes associated with movement of the ISP are more rapid by at least an order of magnitude than the rate of ubiquinol oxidation. (v) Movement of the ISP head does not introduce a significant delay in reduction of the high potential chain by quinol, and it is not necessary to invoke such a delay to explain the kinetic disparity between the kinetics of reduction of cytochromes c1 and bH.

Dynamical relationship of infrared cloudtop temperatures with occurrence rates of cloud‐to‐ground lightning and sprites

We correlated cloudtop temperatures obtained from GOES‐8 infrared images, lightning data from the National Lightning Detection Network, and triangulated nadir positions of sprites from a 22 July 1996 Mesoscale Convective System (MCS) over Kansas. The maximum sprite production of the MCS occurred during the transition between growth and decay phases of the system, and when the occurrence rate of negative cloud‐to‐ground (−CG) flash activity maximized. The −CG flash rate was maximum when the overlying cloudtop temperatures Tc were minimum, −69° to −72°C. During the MCS growth phase, the −CG occurrence rate increased smoothly with decreasing Tc, and declined with increasing Tc during the decay phase. By way of contrast, the +CG rate remained associated with approximately constant Tc (−69° and −72°C) during the growth phase, and then also declined with increasing Tc during the decay phase. The sprite‐generating +CGs occurred in regions with cloudtop temperatures 2–3°C warmer than the rest of the +CG population.

Lightning activity on the central Tibetan Plateau and its response to convective available potential energy

Lightning flash activities on the central Tibetan Plateau have been studied by using the satellite-based Lightning Imaging Sensor (LIS) database from January 1998 to July 2002. The lightning activity shows a clear diurnal variation on the central Plateau. The peak lightning activity appears at about 17: 00 which is 3 h earlier than that in Jingzhou, Hubei in the same latitude belt nearby, indicating that the lightning activity is a sensitive indicator of solar heating on the Plateau. The lightning discharge is weaker on the Plateau than Jingzhou, Hubei and other low-altitude continental regions because of the lower convective available potential energy (CAPE) on the Plateau. The CAPE on the Plateau is 12 times lower than that in Jingzhou, Hubei, and 20 times lower than that in the sea-level region, such as Guangzhou and Florida. However, the sensitivity of lightning activity to CAPE changes on the Plateau is up to 30 times more sensitive than other prominent low-altitude regions.

The convective storm system during IOP 2a of MAP: Cloud‐to‐ground lightning flash production in relation to dynamics and microphysics

AbstractThis paper presents a study about correlation between cloud‐to‐ground lightning flash (CG) activity, and the dynamics and microphysics of thunderclouds. Data collected during Intense Observation Period (MAP IOP) 2a of the Mesoscale Alpine Programme Special Observing Period (SOP) over the Lago Maggiore Target Area (LMTA) in northern Italy are used. IOP 2a was the most electrically active period during the SOP, representing 75% of the total CG activity. Thunderclouds were strongly vertically developed (the 30 dBZ echo tops were sometimes higher than 12 km) and produced large amounts of rainfall and some hail. Doppler and polarimetric radar data allow us to retrieve the three‐dimensional wind and radar‐reflectivity fields from two synchronous Doppler radars, and particle‐type fields in the thunderclouds from the S‐Pol polarimetric radar. Both polarities of CGs are distinguished. Temporal and spatial relationships from the global activity over the LMTA are first studied. Then, the temporal correlation between CG rates and dynamics or microphysics for five individual cells is considered. A very strong correlation is observed between CG and the presence of a mixture of graupel and hail, which strongly supports a non‐inductive charging mechanism. CG impacts seem to be located underneath large radar‐reflectivity values and around the maximum vertical velocities. Two individual cells are studied in more detail, in order to better understand their different electrical behaviours: the first produced mainly negative CGs, and the second produced 61% positive CGs in the second phase of its lifetime. The association of positive CGs with severe weather and especially with the presence of hail is observed. Copyright © 2003 Royal Meteorological Society.

Discovery of the neutron star nature of SLX 1737-282

SLX 1737-282 is a persistent moderately bright X-ray source 12 from the Galactic center. X-ray observations with the Wide Field Cameras on BeppoSAX have for the first time revealed the true nature of SLX 1737-282: a 15 min long thermonuclear flash was detected exposing the source as a neutron star in a binary system. The flash was Eddington-limited constraining the distance to between 5 and 8 kpc. We analyze BeppoSAX, ROSAT, and RXTE data on SLX 1737-282. The persistent 0.5–200 keV luminosity is close to or less than 1% of the Eddington limit which implies a rarely-seen circumstance for thermonuclear flash activity.

Methodologic lessons learned from hot flash studies.

In the course of conducting a series of prospective clinical trials devoted to defining new treatment opportunities for hot flashes in cancer survivors, considerable experience has been acquired with related methodologic issues. This article has been written in response to many queries regarding this methodology. A series of seven different clinical trials that involved 968 patients was used for this work. Reliable and valid definitions of hot flash intensity were developed from patient-reported descriptions. Concomitant validity and reliability assessment of patient-completed diaries was undertaken to compare hot flash data with toxicity and quality-of-life (QOL) end points and to examine consistency across patient groups using variability analysis and correlation procedures. Parametric data from this meta-analysis was used to examine relative power considerations for the design of phase II and phase III clinical trials. Daily diaries used in these studies exhibited consistency and reliability and had few missing data. Hot flash frequency and hot flash score (frequency multiplied by average severity) variables produced almost identical end point results. For phase III placebo-controlled studies, 50 patients per treatment arm seem appropriate to provide sufficient power specifications to detect a clinically meaningful change in hot flash activity. For phase II trials, 25 patients per trial seem to provide reasonable estimates of eventual hot flash efficacy to screen potential agents for more definitive testing. Given the data gained from these experiences, we can plan and carry out more efficient trials to identify efficacious agents for the reduction of hot flash activity.

Diurnal variations of the atmospheric electric field and conductivity at Maitri, Antarctica

Surface measurements of the atmospheric electric potential gradient and conductivity have been made at the Indian station, Maitri (70°45′52″S, 11°44′3″E, 117 m above mean sea level), Antarctica, from January 10 to February 24, 1997. The diurnal variation curve of potential gradient averaged for 20 fair weather days is single periodic with a maximum at 1300 UT and another secondary but distinct maximum at 1900 UT and a minimum at 0100 UT. The mean value of the potential gradient is 83 V m−1 and the maximum and minimum values are 1.55 and 0.73 times the mean value, respectively. The total conductivity is 2.1×10−14 S m−1, and does not show any significant diurnal variation. The diurnal variation of the potential gradient observed at Maitri is similar to the one observed a few days later in the southern Indian Ocean and to the one reported by Kamra et al. [1994] with a few hours difference in phase in the northern Indian Ocean. The results are discussed in terms of the seasonal variation of the longitudinal distribution of thunderstorm activity. It is proposed that the diurnal variation of flash activity when averaged over several days or weeks may cause a peak at an averaged time in the diurnal variation of ionospheric potential.

Site specific labeling of Rhodobacter sphaeroides reaction centers with dye probes for surface pH measurements

Covalently bound pH sensitive dyes are an important tool for characterizing the proteolytic reactions of protein complexes that play key roles in biological energy transduction. Here we demonstrate the feasibility of this method for photosynthetic reaction centers (RCs) for the first time, by the highly selective attachment of two thiol reactive derivatives of fluorescein to the two H subunit cysteines of the photosynthetic RC from Rhodobacter sphaeroides R-26 The p K a shifts of the dyes upon binding to the protein and in response to high salt were measured, and interpreted based on the structure of the RC. 2-[(5-fluoresceinyl)aminocarbonyl]ethyl-methanethiosulfonate was attached to Cys H156 and fluorescein-5-maleimide to Cys H234. By following the absorption changes of bound fluorescein (500 nm), and those of the hydrophilic pH indicator 8-hydroxypyrene-1,3,6-tris-sulfonic acid (468 nm), the surface and bulk pH were monitored separately with less than 5% crosstalk. Flash-induced proton uptake and external calibrations by mixing with aliquots of acid were measured in different redox states of the RCs. The results indicate that the charge in the quinone acceptor complex after flash activation (primary quinone acceptor (Q A) − or secondary quinone acceptor (Q B) −) has no effect on the surface pH and potential in the vicinity of these two attachment sites, between pH 6.5 and 9. Application of the method to other surface locations is discussed.

Some aspects of the correlation between lightning and rain activities in thunderstorms

The lightning activity of convective systems is a sometimes fruitful indicator of their precipitation production. The present study compares rain volume with different types of lightning activity in several convective systems. The study uses data obtained in the Paris area where two lightning detection systems coexist. The Météorage network provides the location and the polarity of cloud-to-ground flashes, while the SAFIR system detects the total flash activity: cloud-to-ground, intra-cloud flashes and VHF individual sources within a given time window. The overall spatial correlation between rain and lightning appears to be very consistent for all lightning types. A pixel-to-pixel study shows that positive CG flashes are associated with higher rainwater volume than negative flashes. Introducing a weight coefficient for positive CG flashes considerably improves the correlation between rain amount and lightning production. Taking into account the specific contribution of each type of lightning flash, the amount of rain can be estimated from the total electrical activity of each system. Comparison with the amount derived from radar measurement shows reasonable agreement. Finally, the parallel time evolutions of rain and lightning rates display quite similar characteristics.

Specific mutagenesis of the rieske iron-sulfur protein in Rhodobacter sphaeroides shows that both the thermodynamic gradient and the pK of the oxidized form determine the rate of quinol oxidation by the bc(1) complex.

In the Rieske iron-sulfur protein (ISP) of the ubiquinol:cytochrome c(2) oxidoreductase (bc(1) complex) of Rhodobacter sphaeroides, residue Tyr 156 is located close to the iron-sulfur cluster. Previous studies of the equivalent residue in both Saccharomyces cerevisiae [Denke, E., Merbitz-Zahradnik, T., Hatzfeld, O. M., Snyder, C. H., Link, T. A., and Trumpower, B. L. (1998) J. Biol. Chem. 273, 9085-9093] and Paracoccus denitrificans [Schroter, T., Hatzfeld, O. M., Gemeinhardt, S., Korn, M., Friedrich, T., Ludwig, B. , and Link, T. A. (1998) Eur. J. Biochem. 255, 100-106] have indicated that mutations at this site can lead to modifications in the redox potential of the ISP. To study the effect of similar modifications on the thermodynamic behavior and kinetics of partial reactions of the bc(1) complex upon flash activation, we have constructed four mutant strains of Rb. sphaeroides where Tyr 156 was mutated to His, Leu, Phe, or Trp. The bc(1) complex was assembled and able to support photosynthetic growth in all mutants. Three substitutions (Leu, Phe, Trp) led to alteration of the midpoint potential (E(m)) of the ISP and a slowing in rate of quinol oxidation, suggesting that electron transfer from quinol to the oxidized ISP controls the overall rate and that this step includes the high activation barrier. The Trp mutation led to an increase of approximately 1 pH unit in the pK value of the oxidized ISP. The pH dependence of the rate of quinol oxidation in this mutant was also shifted up by approximately 1 pH unit, showing the importance of the protonation state of the ISP for quinol oxidation. This provides support for a model in which the dissociated form of the oxidized ISP is required for formation of the enzyme-substrate complex [Ugulava, N., and Crofts, A. R. (1998) FEBS Lett. 440, 409-413].

Normal and mutant rhodopsin activation measured with the early receptor current in a unicellular expression system.

The early receptor current (ERC) represents molecular charge movement during rhodopsin conformational dynamics. To determine whether this time-resolved assay can probe various aspects of structure-function relationships in rhodopsin, we first measured properties of expressed normal human rhodopsin with ERC recordings. These studies were conducted in single fused giant cells containing on the order of a picogram of regenerated pigment. The action spectrum of the ERC of normal human opsin regenerated with 11-cis-retinal was fit by the human rhodopsin absorbance spectrum. Successive flashes extinguished ERC signals consistent with bleaching of a rhodopsin photopigment with a normal range of photosensitivity. ERC signals followed the univariance principle since millisecond-order relaxation kinetics were independent of the wavelength of the flash stimulus. After signal extinction, dark adaptation without added 11-cis-retinal resulted in spontaneous pigment regeneration from an intracellular store of chromophore remaining from earlier loading. After the ERC was extinguished, 350-nm flashes overlapping metarhodopsin-II absorption promoted immediate recovery of ERC charge motions identified by subsequent 500-nm flashes. Small inverted R(2) signals were seen in response to some 350-nm flashes. These results indicate that the ERC can be photoregenerated from the metarhodopsin-II state. Regeneration with 9-cis-retinal permits recording of ERC signals consistent with flash activation of isorhodopsin. We initiated structure-function studies by measuring ERC signals in cells expressing the D83N and E134Q mutant human rhodopsin pigments. D83N ERCs were simplified in comparison with normal rhodopsin, while E134Q ERCs had only the early phase of charge motion. This study demonstrates that properties of normal rhodopsin can be accurately measured with the ERC assay and that a structure-function investigation of rapid activation processes in analogue and mutant visual pigments is feasible in a live unicellular environment.

Cloud‐to‐ground lightning activity and radar observations of storms in the pyrénées range area

AbstractThis paper analyses radar observations and cloud‐to‐ground (CG) lightning flash activity of several thunderstorms occurring over the Pyrénées range during the night of 23‐24 August 1993 and the afternoon of 24 August 1993. the available data consisted of the European meteorological bulletin, the plan position indicator radar scans at three elevations performed by the 5.5 cm wavelength Rodin radar of Toulouse, and the characteristics of the CG lightning strikes.The first thunderclouds began to develop at around 2200 UTC 23 August. Up to 0100 UTC 24 August, we observed three isolated convective cells. We also studied a mesoscale convective system (MCS) occurring during the afternoon of 24 August, and chose to investigate three convective cells embedded within it. These different thunderclouds developed over the Spanish side of the Pyrénées and moved north‐eastwards over the mountains. the locations of CG flashes in relation to the reflectivity fields revealed two kinds of CG lightning activity: flashes associated with intense rainfall, and those located in stratiform cloud areas far from the intense precipitating zone. the flash density was larger within the first type and the positive flash proportion was larger in the second type. the amount of large precipitating particles was characterized by the area A(τ) covered by reflectivities larger than τ dBZ, with τ taken as 33 dBZ. the study of the time evolution of A (33) at three altitudes showed that, for the lightning activity associated with intense rainfall, strong reflectivities at high altitude (4.5 km, and sometimes 7.5 km) coincided with large lightning flash rates, though it was the time evolution of the vertical profile of the area covered by precipitation that drove the CG lightning flash rate (or vice‐versa). the maximum flash rate coincided with the fall of large precipitating particles. Furthermore, a time lag was observed at the ground between the lightning flash rate and the rainfall rate. the time evolutions of the flash rate and A (τ) at the lowest elevation of the radar beam (0.6°) confirmed this delay. the correlation coefficient between these two parameters for the isolated convective cells reached 0.81 in the best case. the correlation between the lightning activity and precipitation of the whole MCS was less good but, nevertheless, the volume of precipitation per CG lightning flash was of the same order of magnitude for all the cells or MCSs observed. It ranged from 3.2 × 103 to 46.8 × 103 m3 flash‐1, in accordance with the results of other authors.

Expression and one-step purification of a fully active polyhistidine-tagged cytochrome bc1 complex from Rhodobacter sphaeroides.

The fbcB and fbcC genes encoding cytochromes b and c1 of the bc1 complex were extended with a segment to encode a polyhistidine tag linked to their C-terminal sequence allowing a one-step affinity purification of the complex. Constructions were made in vitro in a pUC-derived background using PCR amplification. The modified fbc operons were transferred to a pRK derivative plasmid, and this was used to transform the fbc- strain of Rhodobacter sphaeroides, BC17. The transformants showed normal rates of growth. Chromatophores prepared from these cells showed kinetics of turnover of the bc1 complex on flash activation which were essentially the same as those from wild-type strains, and analysis of the cytochrome complement and spectral and thermodynamic properties by redox potentiometry showed no marked difference from the wild type. Chromatophores were solubilized and mixed with Ni-NTA-Sepharose resin. A modification of the standard elution protocol in which histidine replaced imidazole increased the activity 20-fold. Imidazole modified the redox properties of heme c1, suggesting ligand displacement and inactivation when this reagent is used at high concentration. The purified enzyme contained all four subunits in an active dimeric complex. This construction provides a facile method for preparation of wild-type or mutant bc1 complex, for spectroscopy and structural studies.

Evolution of Cloud-to-Ground Lightning Characteristics and Storm Structure in the Spearman, Texas, Tornadic Supercells of 31 May 1990

Abstract On 31 May 1990, four tornadic supercell storms formed sequentially near the intersection of a dryline and an outflow boundary in the northern Texas panhandle. “Staccato” lightning flashes, which have been hypothesized to be positive ground flashes, were observed beneath the anvil of one storm during the most violent tornado that the storm produced. Evidence was found from a lightning mapping system that at least some of the staccato flashes were negative ground flashes. Although the four supercell storms on this day formed in approximately the same area, traveled over roughly the same region, and produced tornadoes and large hail, the relationship between the genesis and evolution of tornadoes and the polarity and flash rates of ground flashes varied widely, as in previous studies. The second of the supercell storms had low-precipitation supercell characteristics; the third and fourth did not. In previously studied storms, ground flash activity in low-precipitation supercell storms has always bee...

Load-dependent mechanical efficiency of individual myosin heads in skeletal muscle fibers activated by laser flash photolysis of caged calcium in the presence of a limited amount of ATP.

Although a contracting muscle regulates its energy output depending on the load imposed on it ("Fenn effect"), the mechanism underlying the load-dependent energy output remains obscure. To explore the possibility that the mechanical efficiency, with which chemical energy derived from ATP hydrolysis is converted into mechanical work, of individual myosin heads changes in a load-dependent manner, we examined the auxotonic shortening of glycerinated rabbit psoas muscle fibers, containing ATP molecules almost equal in number to the myosin heads, following laser flash photolysis of caged calcium. Immediately before laser flash activation, almost all of the myosin heads in the fiber are in the state, M.ADP.Pi, and can undergo only one ATP hydrolysis cycle after activation. When the fibers were activated to shorten under various auxotonic loads, the length, force and power output changes were found to be scaled according to the auxotonic load. Both the power and energy outputs were maximal under a moderate auxotonic load. The amount of M.ADP.Pi utilized at a time after activation was estimated from the amount of isometric force developed after interruption of fiber shortening. This amount was minimal in the isometric condition, and increased nearly in proportion to the distance of fiber shortening. These results are taken as evidence that the efficiency of chemo-mechanical energy conversion in individual myosin heads changes in a load-dependent manner.

The general kinetic model of electron transfer in photosynthetic reaction centers activated by multiple flashes.

A new general kinetic model for the functioning of photosynthetic reaction centers (RC) of purple bacteria, under multiple flash activation, has been developed. The model includes the primary electron donor (P870) as well as the primary (QA) and secondary (QB) acceptor quinones. The new features of this general model include: (1) consideration of four different states of the QB binding site (vacant, occupied by QB, by QB- and by QBH2), (2) incorporation of the dark relaxation of the RC between flashes, (3) the assumption of fast exchange of quinones between the RC and quinone pool in detergent micelles or chromatophore membrane, (4) description of the kinetics of electron transfer in both oxidized (no donor for P870+) and reduced (in the presence of donor for P870+) conditions simultaneously, (5) the consideration of both single and multiple flash activation of the RC of purple bacteria and (6) consideration of the cumulative effects of all previous flashes of the series in the response induced by the current flash. This model is used to calculate and predict (1) flash-induced binary oscillations of the secondary acceptor semiquinone (QB-), (2) flash-induced behavior of P870+ in the presence and absence of electron donor and (3) the apparent equilibrium constant of electron transfer between QA and QB and others. Different characteristics of RC are analyzed as a function of flash intensity, time between flashes, concentration of electron donor, redox-potential of the medium, concentration of pool quinone and quinol, association and dissociation equilibrium constants for quinone and quinol at the QB binding site, equilibrium constants of electron transfer between QA- and QB and between QA- and QB-, as well as the rate constants of oxidation of QA- and QB- by redox mediators. The proposed model can be used as a basis for assays of kinetic behavior of native and mutant RC of purple bacteria and for determination of the factors influencing the release of QH2 from RC. The latter is needed for analysis of factors controlling light-activated electron transport in the cytochrome bc1 complexes of purple bacteria by quinol molecules released from RC. The developed general approach for parallel consideration of flash-induced transitions of RC and its following dark relaxation between flashes can also be used for kinetic description of photosynthetic RC of oxygenic photosynthesis.