Pg Conversion Research Articles

On the Role of a Conserved Tryptophan in the Chromophore Pocket of Cyanobacteriochrome

The cyanobacteriochrome Slr1393 can be photoconverted between a red (Pr) and green absorbing form (Pg). The recently determined crystal structures of both states suggest a major movement of Trp496 from a stacking interaction with ring D of the phycocyanobilin (PCB) chromophore in Pr to a position outside the chromophore pocket in Pg. Here, we investigated the role of this amino acid during photoconversion in solution using engineered protein variants in which Trp496 was substituted by natural and non-natural amino acids. These variants and the native protein were studied by various spectroscopic techniques (UV–vis absorption, fluorescence, IR, NIR and UV resonance Raman) complemented by theoretical approaches. Trp496 is shown to affect the electronic transition of PCB and to be essential for the thermal equilibrium between Pr and an intermediate state O600. However, Trp496 is not required to stabilize the tilted orientation of ring D in Pr, and does not play a role in the secondary structure changes of Slr1393 during the Pr/Pg transition. The present results confirm the re-orientation of Trp496 upon Pr → Pg conversion, but do not provide evidence of a major change in the microenvironment of this residue. Structural models indicate the penetration of water molecules into the chromophore pocket in both Pr and Pg states and thus water-Trp contacts, which can readily account for the subtle spectral changes between Pr and Pg. Thus, we conclude that reorientation of Trp496 during the Pr-to-Pg photoconversion in solution is not associated with a major change in the dielectric environment in the two states.

Selectively Chemocatalytic Conversion of Fructose to 1,2‐Propylene Glycol over Ru‐WOx/Hydroxyapatite Catalyst†

Summary of main observation and conclusionThe conversion of fructose to 1,2‐propylene glycol (PG) is an important process from cellulosic biomass to high‐value added chemicals. Herein, Ru‐WOx/hydroxyapatite (HAP) catalyst was employed for this reaction and reached up to 91.3% yield of PG at 180 °C, 1 MPa initial hydrogen for 8 h in water. On this catalyst, Ru and WOx were highly dispersed on HAP support and they interacted with each other to form a special catalytic center. The lack of isolated Ru or RuW alloy site led to a moderate activity for hydrogenolysis and hindered the further conversion of PG to propanol. The weak basic HAP support efficiently prevented the humin formation. This precisely controlled catalyst has potential in green PG production.

Protochromic absorption changes in the two-cysteine photocycle of a blue/orange cyanobacteriochrome

Cyanobacteriochromes (CBCRs) are phytochrome-related photosensors with diverse spectral sensitivities spanning the entire visible spectrum. They covalently bind bilin chromophores via conserved cysteine residues and undergo 15Z/15E bilin photoisomerization upon light illumination. CBCR subfamilies absorbing violet-blue light use an additional cysteine residue to form a second bilin-thiol adduct in a two-Cys photocycle. However, the process of second thiol adduct formation is incompletely understood, especially the involvement of the bilin protonation state. Here, we focused on the Oscil6304_2705 protein from the cyanobacterium Oscillatoria acuminata PCC 6304, which photoconverts between a blue-absorbing 15Z state ( 15Z Pb) and orange-absorbing 15E state ( 15E Po). pH titration analysis revealed that 15Z Pb was stable over a wide pH range, suggesting that bilin protonation is stabilized by a second thiol adduct. As revealed by resonance Raman spectroscopy, 15E Po harbored protonated bilin at both acidic and neutral pH, but readily converted to a deprotonated green-absorbing 15Z state ( 15Z Pg) at alkaline pH. Site-directed mutagenesis revealed that the conserved Asp-71 and His-102 residues are required for second thiol adduct formation in 15Z Pb and bilin protonation in 15E Po, respectively. An Oscil6304_2705 variant lacking the second cysteine residue, Cys-73, photoconverted between deprotonated 15Z Pg and protonated 15E Pr, similarly to the protochromic photocycle of the green/red CBCR subfamily. Time-resolved spectroscopy revealed 15Z Pg formation as an intermediate in the 15E Pr-to- 15Z Pg conversion with a significant solvent-isotope effect, suggesting the sequential occurrence of 15EP-to-15Z photoisomerization, deprotonation, and second thiol adduct formation. Our findings uncover the details of protochromic absorption changes underlying the two-Cys photocycle of violet-blue-absorbing CBCR subfamilies.

An Investigation into the Conversion of Propylene Glycol to 2,4-dimethyl-1,3-dioxolane over an Acid Catalyst Using Gas Chromatography

In the presence of an acid catalyst, PG react reversibly with acetaldehyde to form 2,4-dim-ethyl-1,3-dioxolane (24DMD). The effects of different operational parameters on PG conversion had been analyzed in paper, parameters included temperature, reaction time, amount of catalyst and aqueous acetaldehyde/PG molar ratio. Under optimal condition, 85% conversion of PG in aqueous solution was achieved within 180 min of reaction. The analysis of PG was conducted by gas chromatograph. Furthermore, reaction followed the second-order reaction kinetics, and the reaction rate constant was found to be 29.68min-1.

Full Time Course Kinetics of the Streptokinase-Plasminogen Activation Pathway

Our previously hypothesized mechanism for the pathway of plasminogen (Pg) activation by streptokinase (SK) was tested by the use of full time course kinetics. Three discontinuous chromogenic substrate initial rate assays were developed with different quenching conditions that enabled quantitation of the time courses of Pg depletion, plasmin (Pm) formation, transient formation of the conformationally activated SK·Pg* catalytic complex intermediate, formation of the SK·Pm catalytic complex, and the free concentrations of Pg, Pm, and SK. Analysis of full time courses of Pg activation by five concentrations of SK along with activity-based titrations of SK·Pg* and SK·Pm formation yielded rate and dissociation constants within 2-fold of those determined previously by continuous measurement of parabolic chromogenic substrate hydrolysis and fluorescence-based equilibrium binding. The results obtained with orthogonal assays provide independent support for a mechanism in which the conformationally activated SK·Pg* complex catalyzes an initial cycle of Pg proteolytic conversion to Pm that acts as a trigger. Higher affinity binding of the formed Pm to SK outcompetes Pg binding, terminating the trigger cycle and initiating the bullet catalytic cycle by the SK·Pm complex that converts the residual Pg into Pm. The new assays can be adapted to quantitate SK-Pg activation in the context of SK- or Pg-directed inhibitors, effectors, and SK allelic variants. To support this, we show for the first time with an assay specific for SK·Pg* that fibrinogen forms a ternary SK·Pg*·fibrinogen complex, which assembles with 200-fold enhanced SK·Pg* affinity, signaled by a perturbation of the SK·Pg* active site.

Platinum/Gold Alloy Nanoparticles-Supported Hydrotalcite Catalyst for Selective Aerobic Oxidation of Polyols in Base-Free Aqueous Solution at Room Temperature

As-prepared platinum/gold alloy nanoparticles-supported hydrotalcites (PtxAuy–starch/HTs) by using a soluble starch as a green reducing and a stabilizing agent are found to be truly effective heterogeneous catalysts for the selective aerobic oxidation of glycerol (GLY) and 1,2-propanediol (PG) in base-free aqueous solution using molecular oxygen in atmospheric pressure at room temperature. The PtxAuy–starch/HTs exhibited higher selectivities for oxidation of the primary hydroxyl group in GLY and PG toward glyceric acid (GA) and lactic acid (LA), respectively, with molecular oxygen in aqueous solution than those reactions over monometallic Pt–starch/HT or Au–starch/HT. Pt60Au40–starch/HT was found to be the most active catalyst for selective aerobic oxidation of polyols. It showed 73% GLY conversion with 57% GA yield and 63% PG conversion with 47% LA yield and retained high selectivity in recycling experiments. XRD patterns of the PtxAuy–starch NPs indicated the d-spacing of Pt atoms was changed by alloyin...

Propylene carbonate synthesis from propylene glycol, carbon dioxide and benzonitrile by alkali carbonate catalysts

The synthesis of propylene carbonate from propylene glycol and carbon dioxide in the presence of various catalysts has been reported. Benzonitrile has been used as both solvent and dehydrating agent. Under optimal conditions, the best results were obtained in the presence of alkali carbonate catalysts. The propylene carbonate yield could reach up to 20% with a propylene-1,2-glycol conversion of 44%. ► Synthesis of PC from PG and scCO 2 in the presence of various catalysts was studied. ► PC yield could reach up 20% with PG conversion of 44%. ► First example reported on direct carbonatation of glycol compounds using benzonitrile. ► Benzonitrile was preferred to acetonitrile to perform reaction for safety reasons.

Synthesis of Propylene Carbonate from Carbon Dioxide and 1,2-Propylene Glycol over Zinc Acetate Catalyst

The synthesis of propylene carbonate (PC) from 1,2-propylene glycol (PG) and CO2 was investigated. Among a series of acetate salts, zinc acetate showed the highest catalytic activity. Under the suitable reaction conditions (reaction temperature, 433 K; weight percentage of catalyst, 2.5%; reaction time, 2 h; molar ratio of acetonitrile to PG, 1.8:1; and initial pressure of CO2, 3.0 MPa), the conversion of PG, the yield of PC, and the selectivity of PC were 19.2%, 12.3%, and 64.1%, respectively. The reaction mechanism for the synthesis of PC from CO2 and PG over zinc acetate catalyst was elucidated by means of gas chromatography-mass spectrometry (GC−MS), in situ infrared (IR) analysis, and X-ray diffraction (XRD) characterization.

Cell Surface Adenosine Deaminase Binds and Stimulates Plasminogen Activation on 1-LN Human Prostate Cancer Cells

Adenosine deaminase (ADA) is expressed intracellularly by all cells, but in some tissues, it is also associated with the cell surface multifunctional glycoprotein CD26/dipeptidyl peptidase IV. By modulating extracellular adenosine, this "ecto-ADA" may regulate adenosine receptor signaling implicated in various cellular functions. CD26 is expressed on the surface of human prostate cancer 1-LN cells acting as a receptor for plasminogen (Pg). Since ADA and Pg bind to CD26 at distinct but nearby sites, we investigated a possible interaction between these two proteins on the surface of 1-LN cells. Human ADA binds to CD26 on the surface 1-LN cells and immobilized CD26 isolated from the same cells with similar affinity. In both cases, ADA binding is diminished by mutation of ADA residues known to interact with CD26. ADA was also found to bind Pg 2 in the absence of CD26 via the Pg kringle 4 (K4) domain. In the presence of 1-LN cells or immobilized CD26, exogenous ADA enhances conversion of Pg 2 to plasmin by 1-LN endogenous urinary plasminogen activator (u-PA), as well as by added tissue Pg Activator (t-PA), suggesting that ADA and Pg bind simultaneously to CD26 in a ternary complex that stimulates the Pg activation by its physiologic activators. Consistent with this, in melanoma A375 cells that bind Pg, but do not express CD26, the rate of Pg activation was not affected by ADA. Thus, ADA may be a factor regulating events in prostate cancer cells that occur when Pg binds to the cell surface and is activated.

Streptokinase Triggers Conformational Activation of Plasminogen through Specific Interactions of the Amino-terminal Sequence and Stabilizes the Active Zymogen Conformation

Cleavage of Arg(561)-Val(562) in plasminogen (Pg) generates plasmin (Pm) through a classical activation mechanism triggered by an insertion of the new amino terminus into a binding pocket in the Pg catalytic domain. Streptokinase (SK) circumvents this process and activates Pg through a unique nonproteolytic mechanism postulated to be initiated by the intrusion of Ile(1) of SK in place of Val(562). This hypothesis was evaluated in equilibrium binding and kinetic studies of Pg activation with an SK mutant lacking Ile(1) (SK(2--414)). SK(2--414) retained the affinity of native SK for fluorescein-labeled [Lys]Pg and [Lys]Pm but induced no detectable conformational activation of Pg. The activity of SK(2--414) was partially restored by the peptides SK(1--2), SK(1--5), SK(1--10), and SK(1--15), whereas Pg(562--569) peptides were much less effective. Active site-specific fluorescence labeling demonstrated directly that the active catalytic site was formed on the Pg zymogen by the combination of SK(1--10) and SK(2--414), whereas sequence-scrambled SK(1-10) was inactive. The characterization of SK(1--10) containing single Ala substitutions demonstrated the sequence specificity of the interaction. SK(1--10) did not restore activity to the further truncated mutant SK(55-414), which was correlated with the loss of binding affinity of SK(55--414) for labeled [Lys]Pm but not for [Lys]Pg. The studies support a mechanism for conformational activation in which the insertion of Ile(1) of SK into the Pg amino-terminal binding cleft occurs through sequence-specific interactions of the first 10 SK residues. This event and the preferentially higher affinity of SK(2--414) for the activated proteinase domain of Pm are thought to function cooperatively to trigger the conformational change and stabilize the active zymogen conformation.

The stimulation of prostaglandin production by two antiprogesterone steroids in human endometrial cells.

Endometrial stromal cells and isolated endometrial glands obtained from women during days 6-26 of the ovarian cycle were cultured for 24 h in the presence of the progesterone antagonists 17 beta-hydroxy-11 beta-[4-dimethylaminophenyl]17 alpha-[1-propynyl] estra-4,9-dien-3-one (RU486) and 17 beta-hydroxy-11 beta-[4-dimethylaminophenyl] 17 alpha-[3-hydroxy-1-propenyl]estra-4,9-dien-3-one (ZK 98734). Both steroids stimulated prostaglandin F2 alpha (PGF2 alpha) production by stromal cells in a dose-dependent manner, in doses ranging from 10-1000 nM. Progesterone (100 nM) inhibited RU486 stimulation, except at the highest dose of antiprogestin. PGE2 was produced in smaller amounts than PGF2 alpha, but, when measurable, it also increased in the presence of RU486. In contrast, RU486 did not increase PG production by endometrial glands. In an experiment to determine the effect of pretreatment, stromal cells were incubated for 24 h with 1000 nM progesterone or RU486 (all with 100 nM 17 beta-estradiol) with either 30 or 6 microM arachidonic acid. These six batches of cells were incubated for a second 24 h with either progesterone or antiprogestin. Cells pretreated with the higher dose of arachidonic acid had a marked increase in PGF2 alpha production during the second 24 h only when also pretreated with progesterone. This finding suggests that progesterone allows an accumulation of PG precursor in a suitable accessible pool. Pretreatment with progesterone also allowed a greater conversion of PG to its 13,14-dihydro-15-keto metabolite. These results suggest that antiprogesterone steroids may act as menstrual regulators by: stimulating endogenous PG production within the endometrial stromal cells and inhibiting PG catabolism.

Estradiol-17β and 2-hydroxyestradiol-17β-induced differential production of prostaglandins by cells dispersed from human intrauterine tissues at parturition

Prostaglandin (PGE, 6-keto PGF 1α) output by cells dispersed from human amnion and decidua in the presence of increasing levels (0–5000 ng/ml) of estradiol-17β (E 2) or 2-hydroxyestradiol-17β (2-OH E 2) was studied in relation to parturition. Tissues were obtained from women at term either before (CS) or after (SL) spontaneous labor and vaginal delivery. In the absence of estrogens, the output of both PGs from amnion increased significantly with labor. No significant increase in decidua PG output occurred with labor. Neither estrogen influenced CS amnion PG output. However, both E 2 and 2-OH E 2 stimulated SL amnion PGE output (2-OH E 2>E 2) while having no affect on 6-keto PGF 1α output. Only the highest dose of 2-OH E 2 stimulated PGE output in CS decidua, but both estrogens significantly inhibited 6-keto PGF 1α output in this tissue. In SL decidua only 2-OH E 2 significantly stimulated PGE, and neither estrogen affected 6-keto PGF 1α output. These results might suggest that estrogens modulate PG biosynthesis at the level of endoperoxide to primary PG conversion.

Photoelectric Studies. VIII. Positional Effect in Photomultipliers and Some Revised Magnitudes in the North Polar Sequence and Harvard Region C 12.

view Abstract Citations (12) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Photoelectric Studies. VIII. Positional Effect in Photomultipliers and Some Revised Magnitudes in the North Polar Sequence and Harvard Region C 12. Eggen, Olin J. Abstract It has been found that the 1P21 photomultiplier varies in sensitivity, depending on its orientation in the earth's magnetic field. This "positional effect" has been eliminated by shielding the photomultiplier with demagnetized strap-iron. The only magnitudes in the previous seven papers of this series that are seriously affected by the positional effect are those in Paper I for the North Polar Sequence. New magnitudes for some of these polar stars have been determined (Table 2). Otherwise no change is required in all other magnitudes in Papers 1-VIl, which are uniformly on a consistent system referred to Harvard Standard Region C 12. A standard radium light-source has been used to control the observations of stars in widely different parts of the sky. Improved magnitudes and colors, Pg and Cp, for the stars in Region C 12 differ at most by 0.02 or 0.03 mag. from the values used in previous papers (Table 1). Equations (1) and (2) give the conversion of Pg and Cp to the system of Stebbins, Whitford, and Johnson, which is based on nine stars of the North Polar Sequence. The change of the zero point in this conversion would make all apparent and absolute magnitudes in Papers 1-vIl fainter by 0.14 mag. Publication: The Astrophysical Journal Pub Date: July 1951 DOI: 10.1086/145458 Bibcode: 1951ApJ...114..141E full text sources ADS | data products SIMBAD (20) Related Materials (6) Part 1: 1950ApJ...111...65E Part 2: 1950ApJ...111...81E Part 3: 1950ApJ...111..414E Part 4: 1950ApJ...112..141E Part 5: 1951ApJ...113..367E Part 6: 1951ApJ...113..663E