Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0031511 (pheochromocytoma)
 14,622 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Biotin is the cofactor of carboxylases [pyruvate (PC), propionyl-CoA (PCC), 3-methyl crotonyl-CoA and acetyl-CoA], to which it is covalently bound by the action of holocarboxylase synthetase (HCS). We have studied whether biotin also regulates their expression, as it does other, nonrelated enzymes (e.g., glucokinase, phosphoenol pyruvate carboxykinase, guanylate cyclase). For this purpose, HCS, PC and PCC mRNAs were studied in biotin-deficient rat liver, kidney, muscle and brain of biotin-deficient rats. PC- and PCC-specific activities and protein masses were also measured. The 24-h time course of HCS mRNA in deficient rats was examined after biotin supplementation. HCS mRNA was significantly reduced during vitamin deficiency. It increased in deficient rats after biotin was injected, reaching control levels 24 h after administration. These changes seem to be the first known instance in mammals of an effect of a water-soluble vitamin on a mRNA functionally related to it. In contrast, the decreased activities of the carboxylases were associated with reductions in the amounts of their enzyme proteins except in brain. However, their mRNA levels were not affected. There are no reports on these types of vitamin affecting the mRNA or protein levels of their apoenzymes or their products. This work provides evidence for biotin being a modulator of the genetic expression of the enzymes involved in its function as a cofactor. As such, it may be a useful model for probing a similar role for other water-soluble vitamins.
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PMID:Biotin regulates the genetic expression of holocarboxylase synthetase and mitochondrial carboxylases in rats. 1143 6

Fatty acid composition of the membrane lipids in the mesophilic cyanobacterium Synechocystis sp. PCC 6803 was altered in earlier work by targeted mutagenesis of genes for fatty acid desaturases. In this work, cells of several mutant strains, depleted in the unsaturated fatty acids in membrane lipids, were grown at 34 degrees C. Spheroplasts (permeabilized cells) were prepared by lysozyme digestion of the cell wall followed by gentle osmotic shock. The bioenergetic parameters ATP formation, electron transport, and H+ uptake were measured at various temperatures. All three bioenergetic parameters for spheroplasts from wild-type cells (which had abundant polyunsaturated fatty acids) were active down to the lowest temperatures used (1 degrees - 2 degrees C). In two strains, which lacked the capacity to desaturate fatty acids at the A 12 position and at the A 12 and A6 positions (designated as desA- and desA-/desD-, respectively), the spheroplasts lost the capacity to form ATP (measured as phenazine methosulfate cyclic phosphorylation) at about 5 degrees C but retained electron transport (water oxidation-dependent ferricyanide reduction) and H+ uptake linked to phenazine methosulfate cyclic electron transport. It appears that the absence of the unsaturation of fatty acids in the A 12 and A6 positions blocks the ability of the photosynthetic membranes to couple a bioenergetically competent proton-motive force to the ATP formation mechanism at temperatures below 5 degrees C. It remains to be determined whether the loss of ATP formation in the mutant strains is the failure of available protons to properly flow into the CF0CF1-ATP synthase or a failure in the CF1 part of the complex in coupling the dissipative H+ flow to the enzyme mechanism of the synthase.
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PMID:Bioenergetic responses of Synechocystis 6803 fatty acid desaturase mutants at low temperatures. 1145 19

Mutation of Glu69 to Gln in the D2 protein of photosystem II is known to lead to a loss of photoautotrophic growth in Synechocystis sp. PCC 6803. However, second-site mutants (pseudorevertants) with restored photoautotrophic growth but still maintaining the E69Q mutation in D2 are easily obtained. Using a genomic mapping technique involving functional complementation, the secondary mutation was mapped to slr0286 in two independent mutants. The mutations in Slr0286 were R42M or R394H. To study the function of Slr0286, mutants of E69Q and of the wild-type strain were made that lacked slr0286. Deletion of slr0286 did not affect photoautotrophic capacity in wild type but led to a marked decrease in the apparent affinity of Ca(2+) to its binding site at the water-splitting system of photosystem II and to a reduced heat tolerance of the oxygen-evolving system, particularly in E69Q. Moreover, a small increase in the half-time for photoactivation of the oxygen-evolving complex of photosystem II for both wild type and the E69Q mutant was observed in the absence of Slr0286. The accumulation of photosystem II reaction centers, dark stability of the oxygen-evolving apparatus, stability of oxygen evolution, and the kinetics of charge recombination between Q(A)(-) and the donor side were not affected by deletion of slr0286. Slr0286 lacks clear functional motifs, and no homologues are apparent in other organisms, even not in other cyanobacteria. In any case, Slr0286 appears to help the functional assembly and stability of the water-splitting system of photosystem II.
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PMID:A novel protein involved in the functional assembly of the oxygen-evolving complex of photosystem II in Synechocystis sp. PCC 6803. 1147 92

A novel and promising method of microcystin-LR (mcyst-LR) degradation is reported. The decomposition of this cyanobacterial toxin using Fenton reagent has been observed with very low initial concentrations of H2O2 and Fe2+ (Fe3+) in the reaction mixture. Mcyst-LR was isolated from a laboratory culture of Microcystis aeruginosa PCC 7813. The initial concentration of the toxin used exceeded by several orders of magnitude those occurring naturally in lakes and drinking water. Even so, the decomposition of the toxin was complete after 30 min.
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PMID:Decomposition of microcystin-LR by Fenton oxidation. 1147 65

The (18)O exchange rates for the substrate water bound in the S(3) state were determined in different photosystem II sample types using time-resolved mass spectrometry. The samples included thylakoid membranes, salt-washed Triton X-100-prepared membrane fragments, and purified core complexes from spinach and cyanobacteria. For each sample type, two kinetically distinct isotopic exchange rates could be resolved, indicating that the biphasic exchange behavior for the substrate water is inherent to the O(2)-evolving catalytic site in the S(3) state. However, the fast phase of exchange became somewhat slower (by a factor of approximately 2) in NaCl-washed membrane fragments and core complexes from spinach in which the 16- and 23-kDa extrinsic proteins have been removed, compared with the corresponding rate for the intact samples. For CaCl(2)-washed membrane fragments in which the 33-kDa manganese stabilizing protein (MSP) has also been removed, the fast phase of exchange slowed down even further (by a factor of approximately 3). Interestingly, the slow phase of exchange was little affected in the samples from spinach. For core complexes prepared from Synechocystis PCC 6803 and Synechococcus elongatus, the fast and slow exchange rates were variously affected. Nevertheless, within the experimental error, nearly the same exchange rates were measured for thylakoid samples made from wild type and an MSP-lacking mutant of Synechocystis PCC 6803. This result could indicate that the MSP has a slightly different function in eukaryotic organisms compared with prokaryotic organisms. In all samples, however, the differences in the exchange rates are relatively small. Such small differences are unlikely to arise from major changes in the metal-ligand structure at the catalytic site. Rather, the observed differences may reflect subtle long range effects in which the exchange reaction coordinates become slightly altered. We discuss the results in terms of solvent penetration into photosystem II and the regional dielectric around the catalytic site.
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PMID:Substrate water exchange in photosystem II depends on the peripheral proteins. 1159 31

Massive growth of cyanobacteria, known as "algal blooms", has become a major concern for water monitoring. It has been observed that environmental factors like temperature, light, and certain patterns of availability of nutrients such as P, N, Fe influence cyanobacterial proliferation and toxin production. In order to monitor nutrients in aquatic ecosystems, an assay for monitoring phosphorus bioavailability to cyanobacteria was developed. The test consists of an immobilized luminescent reporter strain of Synechococcus PCC 7942, designated APL. The reporter strain harbours the gene coding the reporter protein luciferase from Vibrio harveyi under control of the inducible alkaline phosphatase promoter from Synechococcus PCC 7942, and can be induced under phosphorus limitation. The resultant CyanoSensor detects PO(3-)(4)-P in a concentration range of 0.3-8 microM after a sample incubation time of 8 h under continuous illumination (50 microE m(-2) s(-1)). The sensor also responded to a variety of organic phosphorus sources and was storable for 3 weeks at 4 degrees C. It could be demonstrated that the CyanoSensor for bioavailability monitoring is an improvement to conventional phosphorus detection methods.
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PMID:Monitoring of phosphorus bioavailability in water by an immobilized luminescent cyanobacterial reporter strain. 1167 59

A new purification protocol for cytochrome c550 (cyt c550) from His-tagged SYnechocYstis PCC 6803 photosystem II (PSII) was developed which allows the protein to be isolated in high yield and purity. Electron paramagnetic resonance spectroscopy of cyt c550, both free in solution and in intact PSII preparations, yields identical spectra with g values at 1.50, 2.23, and 2.87, which are characteristic for a ferric low-spin bis-histidine coordinated heme. The resonance Raman spectrum of the isolated protein exhibits features characteristic of bis-histidine axial ligation of the iron and a slight ruffling of the heme macrocycle. Together, these results indicate that the heme structure is not very different from most c-type cytochromes, and thus the structure of the heme does not account for its unusually low reduction potential. A direct electrochemical measurement of the reduction potential was performed using square wave voltammetry on a pyrolytic graphite edge electrode, yielding E1.2=-108 mV (vs. NHE) with a peak separation of 5 mV. This value is 150 mV more positive than that previously measured by redox titrations. Because the behavior of the protein in the electrochemistry experiments is indicative of adsorption to the electrode surface, we surmise that binding of the protein to the electrode excludes solvent water from the heme-binding site. We conclude that the degree of solvent exposure makes a significant contribution to the heme reduction potential. Similarly, the binding of cyt c550 to PSII may also reduce the solvent exposure of the heme, and so the direct electrochemical value of the reduction potential may be relevant to the protein in its native state.
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PMID:Factors that determine the unusually low reduction potential of cytochrome c550 in cyanobacterial photosystem II. 1168 4

The purpose of this study was to determine the effect of different cooling methods on thermoregulation before and after intermittent anaerobic exercise in the heat (38 degrees C). On separate days, 10 men completed 4 conditions consisting of 2 sets of six 30-second sprints (with 30 seconds of rest) at 125% of maximal aerobic power with each set of sprints followed by a cooling procedure. The 4 conditions were the following: passive cooling at room temperature (22 degrees C; PRC), fan cooling (4.0 m x s(-1), 22 degrees C; FAC), fan cooling with water spraying (50 ml x min(-1); FWC), and a noncooling passive recovery in the heat chamber (38 degrees C; PCC). Each set of 6 sprints was followed by a 12-minute cooling period; after the second 12-minute period, cooling continued until esophageal temperature (Tes) was reduced by 1.0 degrees C. Tes and mean skin temperatures (Tsk) were taken before and during exercise and during all cooling phases. Cooling rates (mean +/- SEM) after the second set of sprints (based on Tes) were greater (p < 0.05) in PRC (0.043 +/- 0.007) than in the other conditions (FWC = 0.027 degrees +/- 0.005 degrees, FAC = 0.03 degrees +/- 0.004 degrees, and PCC = 0.021 degrees +/- 0.003 degrees C per minute). Overall decreases in heat content, however, were greater in the FWC (-332.2 +/- 27.8) and FAC (-129.9 +/- 14.7 kJ) conditions compared with the PRC condition (29.0 +/- 14.9 kJ). The time required to lower Tes by 1.0 degrees C with PRC (22.8 +/- 1.8) was less than with FAC (30.4 +/- 2.7 minutes). Finally, the rate of increase in Tes during the second set of sprints was less in the FAC and FWC conditions (0.15 degrees +/- 0.01 degrees and 0.11 degrees +/- 0.01 degrees C per minute) compared with the PCC and PRC conditions (0.19 degrees +/- 0.01 degrees and 0.18 degrees +/- 0.01 degrees C per minute), suggesting differences in pre-exercise cooling. Based on cooling rates and the time required to lower Tes by 1.0 degrees C, PRC was the most effective method of cooling. The conclusion is different, however, when taking into account changes in heat content since the FAC and FWC conditions were more effective in dissipating heat and in preventing heat gain during the second set of sprints
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PMID:The influence of different external cooling methods on thermoregulatory responses before and after intense intermittent exercise in the heat. 1171 Apr 12

In oxygenic photosynthesis, photosystem I (PSI) conducts light-driven electron transfer from plastocyanin to ferredoxin. The reactions are initiated when the primary chlorophyll donor, P(700), is photooxidized. P(700) is a chlorophyll dimer ligated by the core subunits psaA and psaB. A difference Fourier transform infrared spectrum, associated with P(700)(+)-minus-P(700), can be acquired using PSI from the cyanobacterium Synechocystis sp. PCC 6803. This spectrum reflects contributions from oxidation-sensitive modes of chlorophyll, as well as from oxidation-induced structural changes in amino acid residues and the peptide backbone. Oxidation-induced structural changes may play a role in the facilitation and control of electron-transfer reactions involving the primary donor. In this paper, we report that photooxidation of P(700) in cyanobacterial PSI perturbs a cysteine residue. At 264 and 80 K, a downshift of a SH stretching vibration from 2560 to 2551 cm(-1) is observed. Such a downshift is consistent with an increase in hydrogen bonding, with a change in C-S-H conformation, or with an electric field effect. Deuterium exchange experiments were also performed. While the perturbed cysteine is in a protein region that is resistant to exchange, other (2)H-sensitive vibrational chl and amino acid bands were observed. From the (2)H exchange experiments, we conclude that photooxidation of P(700) perturbs internal or bound water molecules in PSI and that the P(700)(+)-minus-P(700) spectrum is (2)H exchange-sensitive. The results are consistent with structural complexity in the PSI primary donor, as previously suggested [Kim, S., and Barry, B. A. (2000) J. Am. Chem. Soc. 122, 4980-4981]. Possible explanations, including a partial enolization of P(700)(+), are discussed.
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PMID:A reaction-induced FT-IR study of cyanobacterial photosystem I. 1173 22

The role of D2-Tyr160 (Y(D)), a photooxidizable residue in the D2 reaction center polypeptide of photosystem II (PSII), was investigated in both wild type and a mutant strain (D2-Tyr160Phe) in which phenylalanine replaces Y(D) in the cyanobacterium Synechocystis sp. (strain PCC 6803). Y(D) is the symmetry-related tyrosine that is homologous to the essential photoactive Tyr161(Y(Z)) of the D1 polypeptide of PSII. We compared the flash-induced yield of O(2) in intact, functional PSII centers from both wild-type and mutant PSII core complexes. The yield of O(2) in the intact holo-enzyme was found to be identical in the mutant and wild-type PSII cores using long (saturating) pulses or continuous illumination, but was observed to be appreciably reduced in the mutant using short (nonsaturating) light pulses (<50 ms). We also compared the rates of the first two kinetically resolved steps of photoactivation. Photoactivation is the assembly process for binding of the inorganic cofactors to the apo-water oxidation/PSII complex (apo-WOC-PSII) and their light-induced photooxidation to form the functional Mn(4)Ca(1)Cl(x)() core required for O(2) evolution. We show that the D2-Tyr160Phe mutant cores can assemble a functional WOC from the free inorganic cofactors, but at a much slower rate and with reduced quantum efficiency vs wild-type PSII cores. Both of these observations imply that the presence of Y(D)(*) leads to a more efficient photooxidation of the Mn cluster relative to deactivation (reductive processes). One possible explanation for this behavior is that the phenolic proton on Y(D) is retained within the reaction center following Y(D) oxidation. The positive charge, likely shared by D2-His189 and other residues, raises the reduction potential of P(680)(+)/P(680), thereby increasing the driving force for the oxidation of Mn(4)Y(Z). There is, therefore, a competitive advantage to organisms that retain the Y(D) residue, possibly explaining its retention in all sequences of psbD (encoding the D2 polypeptide) known to date. We also find that the sequence of metal binding steps during assembly of apo-WOC-PSII centers in cyanobacteria cores differs from that in higher plants. This is seen by a reduced calcium affinity at its effector site and reduced competition for binding to the Mn(II) site, resulting in acceleration of the initial lagtime by Ca(2+), in contrast to retardation in spinach. Ca(2+) binding to its effector site promotes the stability of the photointermediates (IM1 and above) by suppressing unproductive decay.
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PMID:A functional role for tyrosine-D in assembly of the inorganic core of the water oxidase complex of photosystem II and the kinetics of water oxidation. 1179 Jan 21


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