Basal Salt Solution Research Articles

Viscometric titration of a linear polyelectrolyte

Viscosities of dilute solutions of linear poly(2-vinyl pyridine) with molecular weights ranging from 3.0×104 to 1.0×106 have been measured under conditions where the polymer can be charged by protonation. By employing weakly acidic solvents, large reduced viscosities typical of polyelectrolytes in low-salt solutions are observed. They exhibit a pronounced maximum occurring at a concentration which is independent of molecular weight. Separate pH titrations are used to calculate polyion charge density and electrostatic screening lengths. The origin of the viscosity maximum is explained by consideration of changing electrostatic persistence lengths on dilution, resulting in polyion coil expansion and contraction. Investigations of limiting conditions of low charge density and full electrostatic screening with basic and high acid or salt solutions reveal expected normal polymer behavior in concentration extrapolations to the intrinsic viscosity.

Human plasma contains low molecular weight factors which stimulate active sodium transport in erythrocytes

The aim of this study was to establish whether differences in sodium efflux rate constants ( K e ) in human erythrocytes occur when artificial media are compared with plasma. Using a 22Na tracer method, a mean total K e of 0.49 ± 0.10 h −1 and significantly ( p < 0.05) lower K e values in Hanks' solution (0.43 ± 0.08 h −1) and Basic Salt Solution (0.37 ± 0.07 h −1) were observed. Exhaustive dialysis of plasma against Hanks' solution over a membrane with relative molecular mass cut-off of 1000 Da resulted in a decrease of the plasma total K e value to that measured in Hanks' solution. After equilibrium dialysis of plasma against Hanks' solution a decrease of total K e was found in plasma and an increase of the K e in Hanks' solution was measured. The data suggest the presence of an excess of dialyzable, active sodium transport stimulating plasma factor(s) with relative molecular mass below 1000 Da.

Development of sheep embryos in vitro in a medium supplemented with different batches of serum albumin.

Variability in different lots of commercial serum albumin affects mammalian embryo development in culture. The composition of commercial preparations of ovine, bovine and defatted bovine serum albumin and a fraction of ovine serum containing proteins with a mean molecular weight of 65 kDa (fraction 3) was examined by polyacrylamide gel electrophoresis. All preparations were heavily contaminated with serum proteins other than albumin. Day-6 sheep morulae were cultured for 48 h in a basal bicarbonate-buffered salt solution supplemented with the commercial preparations of ovine, bovine or defatted bovine serum albumin. These three albumin preparations differed in their abilities to support the development of morulae into expanded blastocysts, but these differences disappeared when the basal medium was also supplemented with a component of ovine serum containing substances with molecular weights of less than 10 kDa. In the latter case, the three commercial albumin preparations and fraction 3 of ovine serum all supported full development in about 40-60% of morulae.

Effects of low-molecular-weight fractions (LMWF) from milk, egg yolk, and seminal plasma on freezability of bovine spermatozoa

The effects of the dialyzable fractions from bovine seminal plasma, egg yolk, and milk and of two buffer systems (TEST and sodium citrate) on post-thaw sperm motility were studied. Each basic salt solution was used in the experimental design. These solutions were used as extender systems in combination with egg yolk and glycerol. After collection, semen samples were extended (1:20), cooled to 5 °C in 1.5 hr, and frozen in 0.5-cc French straws after 3 hr of equilibration. Post-thaw samples were assayed for percentage of motile cells immediately after thawing and after 4 hr of incubation at room temperature (22 °C). Egg yolk (25%) provided the same protection as did the combination of colloidal material present in the skim milk-yolk extenders. The use of TEST as a buffer provided significantly higher ( P < 0.01) sperm post-thaw motility than milk salts or Na citrate. Sperm survival in extenders containing high concentrations of seminal plasma and/or egg yolk salts was significantly lower ( P < 0.01). Spermatozoa frozen in the presence of 6% glycerol resulted in sperm motility significantly ( P < 0.05) higher than that of spermatozoa frozen with 3% glycerol. However, no difference was observed between these two concentrations when TEST solution was used.

Uptake of 2-β- d-ribofuranosylthiazole-4-carboxamide (Tiazofurin) and analogues by the facilitated transport mechanism of erythrocytes

Tiazofurin (TR), a new antitumor agent, enters human erythrocytes by utilizing their facilitated nucleoside transport system. TR competes with endogenous nucleosides for this transport mechanism, thereby reducing nucleoside uptake into the cells. Pre-incubation of erythrocytes for 10 min at 22°C with 100 μM and 500 μM TR reduced the transport of 14C-uridine into the cells by 27% and 74%, respectively. Simultaneous exposure of cells to TR and [ 14C]uridine did not alter the inhibitory effect of TR. Furthermore, the transport inhibitory effect of TR was lost when cells were washed twice with Hanks basal salt solution following a 10-min pre-incubation with TR. The K m and V max (±S.E.) for radiolabeled TR transport into erythrocytes are 170 ± 26 μM and 55 ± 13 nmol/h per 10 6 cells, respectively, which is similar to the kinetic constants measured for uridine transport into erythrocytes ( K m = 168 ± 37 μM and V max = 61 ± 16 nmol/h per 10 6 cells). The K i (±S.E.) of TR for uridine transport is 178 ± 11 μM and for thymidine transport is 102 ± 59 μM. Three analogues of TR (its selenium isostere (SR), and Ara (Ara-TR) and Xylo (Xylo-TR) derivatives) were compared with TR for their ability to compete with and inhibit uridine transport, as these analogues were not available in a radiolabeled form for direct measurement of their transport into the cell. SR had similar kinetic characteristics of inhibition of uridine transport to TR ( K i = 145 ± 15 μM) but Ara-TR had a K i = 1.04 ± 0.13 mM while Xylo-TR inhibited uridine transport with a K i = 1.57 ± 0.67 mM. Thus, TR is transported into erythrocytes with the same velocity and affinity for the carrier as uridine and competitively inhibits nucleoside transport into the cell. Of 3 other C-nucleoside derivatives examined, SR is of similar potency to TR but Ara-TR and Xylo-TR are much less effective at competing with uridine for the nucleoside transporter.

Macromolecular Synthesis in Leishmania donovani Amastigotes

Amastigotes (non-flagellated tissue forms) of Leishmania sp. reside and multiply within the phagolysosomes in tissue macrophages of vertebrate hosts. They are true obligate, intracellular parasites and do not persist as viable entities outside of host cells. This absolute dependence on host cells raises interesting questions about the metabolic capabilities of the amastigote stage. It is assumed that in general, intracellular stages of parasitic protozoa, exhibit reduced metabolic capabilities when compared with insect or culture forms. This hypothesis is largely untested in Leishmania sp. although there is evidence to indicate that several enzymes in amastigotes are less active than their counterparts in promastigotes (Coombs et al., 1982, Molecular and Biochemical Parasitology 5: 199-211; Meade et al., 1984, Journal of Protozoology 31: 156-161). Both forms also differ in their ability to utilize various substrates (Hart et al., 1981, Molecular and Biochemical Parasitology 4: 39-51; Hart and Coombs, 1982, Experimental Parasitology 54: 397-409). The presence of several enzymes of intermediary metabolism in amastigotes of L. donovani (Looker et al., 1983, Molecular and Biochemical Parasitology 9: 15-28; Meade et al., loc. cit.) and L. mexicana (Coombs et al., 1982, loc. cit.) suggests that they are indeed capable of carrying out independent metabolic activities. Since in vitro demonstration of enzyme activity in cell free extracts in and of itself does not ensure functional activity in vivo, the capacity of L. donovani amastigotes to catabolize and incorporate substrates or precursors into macromolecules was tested. Amastigotes of L. donovani (Sudan strain 1S) were isolated and purified from infected hamster spleens as described before (Meade et al., 1984, loc. cit.). Parasites were washed twice and resuspended in basal salts solution (Mukkada et al., 1974, Journal of Protozoology 21: 393-397), pH 5.5 to a density of 0.35 mg protein/ml. Incorporation of glucose and proline into macromolecules was determined by measuring the incorporation of label into cold trichloroacetic acid (TCA) insoluble materials (Mukkada and Simon, 1977, Experimental Parasitology 42: 87-96). Amastigote suspensions (4.9 ml) were incubated on a shaking waterbath at 30 C for 20 min for temperature equilibration. [U-_4C]D-glucose and [U-_4C]-L-proline were added to a final concentration of 0.1 mM and a specific radioactivity of 0.4 A,Ci/umole. Samples of 0.5 ml were withdrawn at various intervals and immediately added to 0.5 ml cold 10% TCA. After 15 min of extraction, 0.5 ml of the suspension was filtered through a millipore filter (0.8 ,tm porosity), washed with 3 ml basal salts and the filter pads with the cells thereon were dropped into scintillation vials containing 10 ml Bray's solution (Bray, 1960, Analytical Biochemistry 1: 279-285); radioactivity was determined in a Packard scintillation spectrometer Model 3003. Radioactivity in amastigotes after extraction with cold TCA represents incorporation of label into macromolecules. Synthesis of nucleic acids was followed by determining the incorporation of [3H] thymidine and [3H] uridine into TCA insoluble materials. Amastigote suspensions were incubated with [3H] thymidine and [3H] uridine at a final concentration of 0.4 mM and specific radioactivity of 0.6 ACi/,umole. Samples of 0.5 ml were withdrawn at intervals, filtered rapidly through glass microfiber filters (1.2 ,um porosity; Whatman GF/C) and immediately washed with 3 ml cold 10% TCA. They were then rinsed with 1 ml ethanol (95%) and transferred to vials containing 10 ml Biofluor scintillation fluid (NEN) and the radioactivity determined. Protein was determined by the method of Oyama and Eagle (1956, Proceedings of the Society of Experimental Biology and Medicine 91: 305-307). Since amastigotes were found to carry out a variety of metabolic activities optimally at pH 5.0-5.5 (data not shown) these studies were conducted at pH 5.5. Label from glucose and proline were readily incorporated into TCA insoluble materials in a time dependent fashion (Fig. 1). Though details are not shown, trapping in methyl benzethonium hydroxide (Weiss et al., 1967, Nature 213: 1020-1022) showed the evolution of significant amounts of labelled CO2 from both substrates which clearly indicate that amasti-

Impairment of induction of Δ-aminolevulinic acid synthase by gluconeogenic amino acids and carbohydrates in vitro

This study was undertaken in a system of chick embryo liver cells incubated in Earle's Basal Salt Solution with hormones. Impairment of induction of Δ-aminolevulinic acid synthase (ALAS) by allyl-isopropylacetamide (AIA) was observed in the presence of glucose. Fructose and various gluconeogenic substances including gluconeogenic amino acids had a similar effect. Leucine, which is purely ketogenic, did not influence induction of ALAS. SH-containing amino acids increased induction of ALAS by AIA. The glucose analogues 3-0-methylglucose and 2-deoxyglucose did not impair induction of ALAS by AIA. The inhibitory effect of glycerol, fructose, and glycine was not affected by 3-0-methylglucose but was reversed by 2-deoxyglucose. The results indicate that the salutory effects of proteins on acute attacks of hepatic porphyria are probably caused by their gluconeogenic properties and that glucose-6-phosphate, or a metabolite of glucose-6-phosphate that is not in the glycolytic pathway, is the active agent that leads to the glucose-like effect.

Development of a medium for in vitro culture of oocytes from the polychaeteNereis virens

A culture medium was developed that allowed the maintenance and growth of oocytes from the marine polychaeteNereis virens. The ionic composition of the basic salt solution and the medium was similar to that ofNereis coelomic fluid and had a total osmolarity of 920 mOsm. Longevity and the growth of cultured oocytes were investigated with respect to the presence of amino acids andNereis vitellin in the medium. Some oocytes survived for up to 6 wk. In vitro growth occurred at a rate of about 1 μm diam/d (15°C) and cultured cells seemed morphologically and ultrastructurally normal.

Schistosoma mansoni: Morphologic Changes Induced by Maintenance In vitro

Adults of Schistosoma mansoni were incubated in several culture media at various time intervals ranging from 2 to 96 hr. The morphologic changes induced by the incubation were documented using both scanning and transmission electron microscopy. These included changes in the tegument, esophageal cells, and cecum. Variability was noted among worms within experimental groups and the surface changes on single worms were frequently observed to have patchy distribution. Based on morphologic changes observed, culture media were ranked as adequate, mediocre, or inadequate. RPMI-1640 + 50% fetal calf serum, Eagle's MEM with Earle's salts (no serum), and McCoy's 5A Medium + serum were judged adequate. Basal Eagle's Medium, Triple Eagle Medium, NCTC-135, and Earle's Balanced Salt Solution (all with or without serum) were judged mediocre. Hanks' Basal Salt Solution (with or without serum) was judged as severely inadequate. All media tested gave better results in the presence of serum. These factors point to the necessity for the use of carefully selected culture media, as well as adequate controls and sampling techniques in the interpretation of in vitro experiments with S. mansoni.

Human Plasma and Amino Acids as Moderators of Uptake and Metabolic Consequences of Antifolates in WIL-2 and Human Leukemia Cells&lt;xref ref-type="fn" rid="FN2"&gt;2&lt;/xref&gt;

Plasma and medium composition significantly affect cellular association of the lipid-soluble antifolate 2,4-diamino-5-(3',4'-dichlorophenyl)-6-methylpyrimidine (DDMP). This was demonstrated by measuring association of labeled drug with cells and by assaying the antimetabolic effect of DDMP on incorporation of deoxyuridine into DNA. Uptake of both aqueous and lipid-soluble antifolates was substantially reduced in the human lymphoblastoid cell line WIL-2 when Eagle's minimum essential medium (EMEM) was substituted for a basal salts solution containing glucose [DDMP approximatley 50%, methotrexate (MTX) approximately 30%]. Uptake of DDMP, however, was inhibited by the amino acid fraction of EMEM or glutamine alone, whereas MTX uptake was unaffected by amino acids. Further studies with human leukemia cells showed that DDMP was only about 25% as effective an inhibitor of deoxyuridine incorporation in autologous human plasma when compared to its inhibitory effect in RPMI-1640 medium MTX inhibition of deoxyuridine incorporation in these cells was essentially unaffected by substitution of autologous human plasma for RPMI-1640 medium. Replacing EMEM with pooled human plasma resulted in a 60-70% decrease in DDMP uptake but had only a marginal effect upon MTX uptake. Thus the choice of medium is important in studies of lipid-soluble antifolates such as DDMP that have a high affinity for cellular and medium lipoprotein components.

Characterization of organic nitrogen in natural waters: Its molecular size, protein content, and interactions with heavy metals

The nitrogenous organic matter from two freshwater lakes and from the filtrate of a unialgal culture of Anabaena sp. was characterized chemically and evaluated for metal complexation ability. Proteinaceous matter was isolated from acidified samples by cellulose cation exchange columns and eluted with a basic salt solution. Isolated proteinaceous matter accounted for 14–34% of the original dissolved organic nitrogen. Gel permeation chromatography and ultrafiltration methods used to separate dissolved organic nitrogen into various size fractions yielded differing results, but most of the organic nitrogen had apparent molecular weights between 10,000 and 50,000 daltons. The copper‐complexing capacity of the proteinaceous matter was determined by differential pulse anodic stripping voltammetry. Conditional stability constants, which represent the mixed stability of all nonlabile ligands in the sample, ranged from 1.6 × 106 to 1.3 × 107 for the three samples.

The influence of incubation conditions on the rates of juvenile hormone biosynthesis by corpora allata isolated from adult females of the beetle Tenebrio molitor

Radiochemical techniques have been developed for the measurement of juvenile hormone (JH) biosynthesis by isolated corpora allata (CA) from adult female Tenebrio molitor. The method has sufficient sensitivity, using precursor of only approx. 27 mCi/mmole (1 GBq/mmole), to permit measurement on single CA, and can therefore be used to explore the relationship between CA activity and ovarian development in this species. Identification of the hormone, 2E,6E- C 16 JH has been confirmed by a combination of radio-TLC and capillary column radio-GC of the major product of the reaction and its ‘methoxyhydrin’ derivative. No incorporation into either C 17- or C 18-JH was found. A 1:1 stoichiometry between incorporation of [ methyl- 14C]-methionine and [ 3H]-farnesenic acid moieties demonstrates that this amino acid can be used as a mass marker to quantify JH biosynthesis in this species. It has been shown that the rate of hormone biosynthesis is reasonably constant for up to 3 hr after isolation and the influence of pH and methionine concentration have been determined. High rates of hormone production were found when CA were incubated in TC-199, special MEM, and fortified Hanks' basal salt solution, but comparatively low rates of biosynthesis were observed when glands were incubated in Grace's Lepidopteran medium, Schneider's Drosophila medium, and in a medium used by others for the culture of ovaries and prothoracic glands from T. molitor. The CA of adult female T. molitor are activated as early as 48 hr after the pupal-adult moult. Thereafter, high rates of C 16JH synthesis can be demonstrated in isolated glands.

Calcium rather than cyclic AMP as the physiological intracellular regulator of prolactin release.

Studies on the mechanisms which govern the release of prolactin were undertaken using two in vitro techniques. A dispersed preparation of rat anterior pituitary cells was made by mechanical means in the presence of trypsin. These washed cells were drawn up into a small column together with a Bio-Gel matrix and perifused with Earle’s basic salt solution. The eluates containing prolactin were then collected at short intervals. Test substances were added to the perifusion medium and their effect on prolactin release was measured. The results of these studies were compared with those obtained by incubating hemipituitary glands in Medium 199 to measure the effect of test substances on the release of radioimmunoassayable prolactin. Perifusion of dispersed pituitary cells with dopamine produced a marked inhibition of prolactin release within 3 min, and maximal suppression was noted 11 min after initiating the perifusion. Upon withdrawal of dopamine, prolactin release began to recover within 1 min and continued to rise to 80% of baseline at 6.5 min. Perifusion of pituitary cells in medium free of calcium also produced a marked reduction in prolactin release which was restored after reexposure of the cells to calcium. The addition of manganese and D-600, agents which block calcium channels, also caused reversible inhibition of prolactin release. The effects of the ionophores A23187 and X537A on prolactin release were studied. The presence of calcium ionophore A23187 did not effect prolactin release but it reversed the dopamine-mediated inhibition of prolactin release. In the absence of calcium, both ionophores stimulated release of prolactin. Tetrodotoxin, a blocker of sodium channels had no effect on prolactin release. Agents such as prostaglandin E₁, and cholera toxin increased cyclic AMP levels, but no positive correlation was obtained on prolactin release patterns. Gpp(NH)p-stimulated adenylate cyclase activity in homogenates of anterior pituitary tissue was unaffected by dopamine. In contrast, addition of dibutyryl cyclic AMP to perifused pituitary glands stimulated prolactin release and theophylline added to hemipituitary gland completely reversed the inhibitory effect of dopamine on prolactin release and caused a concomitant increase in cyclic AMP levels. It is suggested that the tonic high level of prolactin release is maintained by influx of extracellular calcium and that dopamine inhibits this process. The role of intracellular cyclic AMP is undefined; however, the effects of dibutyryl cyclic AMP and theophylline may be due to mobilization of intracellular calcium and thereby stimulate prolactin release by this mechanism rather than through cyclic AMP. In summary, we present evidence that regulation of prolactin secretion by normal lactotropes is a calcium-mediated process.

GABA influences rabbit corneal deturgescence

GABA and its analogues were shown to stimulate the rabbit corneal endothelial fluid pump in the micromolar range. GABA increases the rate of fluid pumping when added to the basic salt solution. The stimulation was abolished by bicuculline and chlorpromazine. The efficacy of GABA and the survival time markedly increased in the presence of insulin and glucose, in presumably physiological concentrations. Complete reversal and survival up to 8 hours is obtained by GABA-glucose-insulin combination, whereas the glutathione-glucose-insulin combination is not efficient.

Affinity chromatography of rabbit liver beta-glucuronidase.

An affinity adsorbent was prepared by coupling p-aminophenyl 1-thio-β-D-gluco-pyranosiduronic acid with CH-Sepharose 4B. β-Glucuronidase from rabbit liver was adsorbed on p-aminophenyl 1-thio-β-D-glucopyranosiduronic acid-CH-Sepharose then eluted with basic buffer or salt solution. The specific enzyme activity increased 46-fold and essentially all of the activity of the enzyme was recovered in elution buffer containing 0.1M NaCl. N-Acetyl-β-glucosaminidase was adsorbed slightly but β-glucosidase and β-galactosidase were not adsorbed on the affinity adsorbent. The adsorbent retained affinity for the enzyme after being used ten times.

Factors in the Movement of Hexose across the Intestine of Ascaris suum

Trichloroacetic acid extractable carbohydrate of the intestine of Ascaris suum decreases rapidly when ribbons of the tissue are incubated in a basal salt solution. After 10 min incubation endogenous carbohydrate is 32% and after 80 min it is 19% of the "zero" time control value. In contrast, there is approximately a 2-fold increase in the endogenous carbohydrate of tissue that is incubated in saline with glucose. The increase occurs within the first 5 min and is maintained throughout an 80-min incubation period. Sac preparations of the intestine that are preincubated with glucose and incubated without glucose move 3-0-methylglucose from the luminal to the pseudocoelomic fluid at a rate that is comparable initially to the rate of movement measured for sac preparations that are incubated in saline with glucose. After 10 min the rate decreases. The addition of glycogen or trehalose to the saline bathing the pseudocoelomic side of sac preparations does not facilitated the movement of 3-0-methylglucose. Collectively, the results support the suggestion that the limited movement of 3-0-methylglucose across intestinal sac preparations that are incubated without glucose is due to the tissue's limited carbohydrate reserve and its rapid depletion in vitro.

わが国の沿岸海域における炭化水素酸化細菌に関する生態学的研究-I

Little has been known as yet of the ecology of hydrocarbon-oxidizing bacteria in Japanese coastal waters such as the Inland Sea where various petrolic and organic pollutants are abundantly poured. Therefore, a series of studies has been undertaken to make it clear. To start with, some methods to enumerate hydrocarbon oxidizers in these areas have been examined in this paper, and results obtained can be summarized as follows. As suitable organic and nitrogen sources for hydrocarbon oxidizers in the surveyed regions, L-alanine and ammonium chloride are recommended respectively. Each liquid medium in which the said suitable organic or inorganic nitrogen source, the basal salt solution and the appropriate hydrocarbon substrate are contained, is tentatively named Medium A or B, and then hydrocarbon oxidizers which are cultured in Medium A or B is designated Group A or B, respectively. The approximate numbers of hydrocarbon oxidizers of both groups in samples if marine materials are enumerated by means of minimum dilution technique, and their accurate numbers are enumerated by means of the minimum dilution technique, and both cases hydrocarbon oxidizers are determined to be existent on the basis that the substrate in the cultured fluid decreases remarkably, which was measured by a gas chromatographic procedure. Emulsification of the fluids incubated in both media, and the decrease in pH value of the fluid in only Group B, are recognized as the supplementary criteria for indicating the existence of hydrocarbon oxidizers in the inocula such as sea water and bottom sediments.

Biosynthesis of purple membrane: control of retinal synthesis by bacterio-opsin

as follows: 500 ml 230 medium 100 reciprocating movements per min for 5 days at Low purple membrane production is observed under conditions of sufficient aeration: cells were grown in Erlenmeyer flasks containing only 90 ml medium under otherwise in the presence of mM nicotine yielded cells with ml medium) or (90 ml of bacteria-opsin, respectively (‘nicotine [7 ] Basal salt solution contained liter 250 g NaCI, 20 g MgSO‘, . 7Ha 0 and 2 g KCl.

Control of mitogen-induced transformation: Characterization of a splenic suppressor cell and its mode of action

The present study demonstrates that mouse spleen cells contain a population of glass wool adherent T lymphocytes which exhibit the capacity to suppress non-glass adherent lymphocyte responses to mitogens. These suppressor cells are stimulated by both low and high doses of PHA 1 1 Abbreviations used: Act. D, actinomycin D; ATS, anti-thymocyte antisera; C′, guinea pig complement; con A, concanavalin A; Bu 2cAMP, dibutyryl cyclic 3′,5′-adenosine monophosphate; HBSS, Hank's basic salt solution; GAL, glass-adherent lymphocytes; NAL, non-glass adherent lymphocytes; PHA, phytohemagglutinin; Mit. C, mitomycin C; [ 3H] Tdr, [ 3H]thymidine; MEM, minimum essential medium; FCS, fetal calf serum. and high doses of con A. The suppressor cell effect is observed when UNA, but not RNA or protein synthesis, is studied. This glass-adherent suppressor cell population is characterized as being the primary DNA synthesizing cells during the early (0–8 hr) stages of culture. Suppression still occurs when the suppressor cells are treated with mitomycin C, actinomycin D or cycloheximide. This implies that new macromolecular synthesis may not be required for suppression to occur. Suppression is blocked by inhibiting synthesis of prostaglandin and is mimicked by Bu 2cAMP. This suggests that mitogen activated suppressor cells regulate T cell responses via production of prostaglandin which modulates the concentration of intracellular cyclic nucleotide levels.

Arrhenius parameters of phototransients in Halobacterium halobium in physiological conditions.

Halobacterium halobium is indigenous to warm saline pools exposed to bright sunlight. Strains of this bacterium synthesise a purple pigment in the cell membrane (the ‘purple membrane’). A single protein, bacteriorhodopsin, is responsible for this characteristic colour, possessing a broad band in the visible spectrum with a maximum at 570 nm (refs 1–3). Pigmented cells utilise solar radiation absorbed by bacteriorhodopsin to create a transmembrane proton gradient which serves as an energy source for ATP synthesis4,5. Most information about the mechanism of operation of this light-driven proton pump has been obtained from spectrophotometric studies of suspensions of purple membrane fragments6–10. We report here a continuation of studies initiated in this laboratory using modulation excitation11 and conventional flash photometry12,13, in which we use the latter technique to observe transient spectral changes in aqueous suspensions of intact cells at physiological temperatures and salinity (basal salt solution).