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Query: UMLS:C0027960 (mole)
 21,279 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A preparation is described through which large quantities of pure, active cytochrome b6/f complex can be isolated from spinach chloroplasts. The resulting complex is at least 90% pure with respect to the maximum content of redox centers, consists of four polypeptides according to polyacrylamide gel electrophoresis, and lacks both ferredoxin: NADP+ oxidoreductase and the high molecular weight form of cytochrome f seen in some other preparations. The complex contains 2 mol b6 and 2 atoms of nonheme iron per mole of cytochrome f, and possesses a high plastoquinol-plastocyanin oxidoreductase activity (Cyt f turnover no. 20-35 s-1). The present preparation should be helpful in the effort to crystallize the cytochrome b6/f complex.
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PMID:Large-scale purification of active cytochrome b6/f complex from spinach chloroplasts. 381 55

A new iron-sulfur protein, distinct from the soluble chloroplast ferredoxin, was isolated from chloroplast membranes. The isolated protein, purified to homogeneity, had a molecular weight of about 8000 and 4 atoms of iron and 4 inorganic sulfides per mole. Its absorption spectrum had a broad absorbance band in the 400 nm region, a shoulder at approximately 310 nm, and a peak around 280 nm. The absorbance ratio A(400) to A(280) was 0.55. The electron paramagnetic resonance spectrum (measured at 12 degrees K) of the reduced protein was similar to that of other reduced iron-sulfur proteins, showing a major resonance line at g = 1.94. The isolated protein, when photoreduced by spinach chloroplasts, can in turn transfer electrons to mammalian cytochrome c. However, the photoreduced protein cannot replace soluble ferredoxin in NADP(+) reduction because of its apparent inability to interact with the chloroplast enzyme, ferredoxin-NADP(+) reductase. The relation of the isolated iron-sulfur protein to the bound ferredoxin that acts as the primary electron acceptor in Photosystem I is discussed.
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PMID:The isolation and characterization of a new iron-sulfur protein from photosynthetic membranes. 436 63

Historically, the role of light in photosynthesis has been ascribed either to a photolysis of carbon dioxide or to a photolysis of water and a resultant rearrangement of constituent atoms into molecules of oxygen and glucose (or formaldehyde). The discovery of photophosphorylation demonstrated that photosynthesis includes a light-induced phosphorus metabolism that precedes, and is independent from, a photolysis of water or CO(2). ATP formation could best be accounted for not by a photolytic disruption of the covalent bonds in CO(2) or water but by the operation of a light-induced electron flow that results in a release of free energy which is trapped in the pyrophosphate bonds of ATP. Photophosphorylation is now divided into (a) a non-cyclic type, in which the formation of ATP is coupled with a light-induced electron transport from water to ferredoxin and a concomitant evolution of oxygen and (b) a cyclic type which yields only ATP and produces no net change in the oxidation-reduction state of any electron donor or acceptor. Reduced ferredoxin formed in (a) serves as an electron donor for the reduction of NADP by an enzymic reaction that is independent of light. ATP, from both cyclic and noncyclic photophosphorylation, and reduced NADP jointly constitute the assimilatory power for the conversion of CO(2) to carbohydrates (3 moles of ATP and 2 moles of reduced NADP are required per mole of CO(2)).Investigations, mainly with whole cells, have shown that photosynthesis in green plants involves two photosystems, one (System II) that best uses light of "short" wavelength (lambda < 685 nm) and another (System I) that best uses light of "long" wavelength (lambda > 685 nm). Cyclic photophosphorylation in chloroplasts involves a System I photoreaction. Noncyclic photophosphorylation is widely held to involve a collaboration of two photoreactions: a short-wavelength photoreaction belonging to System II and a long-wavelength photoreaction belonging to System I. Recent findings, however, indicate that noncyclic photophosphorylation may include two short-wavelength, System II, photoreactions that operate in series and are joined by a "dark" electron-transport chain to which is coupled a phosphorylation site.
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PMID:The light reactions of photosynthesis. 440 Feb 51

Methylene hydroxylation by cytochrome P-450(cam) (cytochrome m) can be resolved into four distinct steps: substrate addition, m(o) --> m(os); reduction, m(os) --> m(rs); dioxygen addition, m(rs) --> m(O2) (rs); followed by a second putidaredoxin (Pseudomonas putida ferredoxin)-mediated reduction and product formation. The isolated ferrous oxy-substrate complex exhibits first-order decay kinetics with the relatively slow rate constant of k [unk] 0.01 sec(-1), at 25 degrees , without product release. Putidaredoxin addition accelerates the decomposition with second-order kinetics, k [unk] 51,000 M(-1) sec(-1), and initiation of product formation. Cytochrome m forms a complex with putidaredoxin with dissociation constant of K(D) = 3 muM. In the complete three-protein hydroxylase system, consisting of cytochrome m, putidaredoxin, and the reductase (a DPNH-specific flavo-protein), camphor hydroxylation occurs with a stoichiometry of 1 mole each of DPNH and O(2) used per mole of product formed; the K(M) for putidaredoxin is about 4.2 muM.Putidaredoxin, on treatment with carboxypeptidase A, loses one molecule each of tryptophan and glutamine sequentially from the carboxy terminus to expose a terminal arginine. The tryptophan-free product has been separated from native putidaredoxin and other impurities, and retains the visible and electron paramagnetic resonance spectra and the redox potential of the active center of native putidaredoxin. This modified redoxin binds less tightly to cytochrome m, K(D) [unk] 150 muM, and is 50 times less effective in stimulation of the m(O2) (rs) decay rate. A similar decrease in specific activity is observed in the complete hydroxylase system.
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PMID:A role of the putidaredoxin COOH-terminus in P-450cam (cytochrome m) hydroxylations. 453 Feb 69

Ferredoxin from Bacillus polymyxa contains (per mole) four non-heme iron residues, four acid-labile sulfide residues, and four cysteine residues. Its molecular weight is approximately 8,800, and it has an oxidation-reduction potential (E(m)) of -390 mv. It is active as an electron carrier in several ferredoxin-linked enzyme systems.
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PMID:Four-iron (sulfide) ferredoxin from Bacillus polymyxa. 503 Jun 19

Mixing between ferredoxin, Fd, and chlorophyll, Chl, occurs at an airwater interface. A complex is formed between the two in the mole ratio 2 Fd:1 Chl. The complex bleaches in light with a quantum yield of 0.4.
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PMID:Interactions between ferredoxin and chlorophyll in a model membrane system. 503 35

The mechanism of ammonia assimilation in Methanosarcina barkeri and Methanobacterium thermoautotrophicum was documented by analysis of enzyme activities, 13NH3 incorporation studies, and comparison of growth and enzyme activity levels in continuous culture. Glutamate accounted for 65 and 52% of the total amino acids in the soluble pools of M. barkeri and M. thermoautotrophicum. Both organisms contained significant activities of glutamine synthetase, glutamate synthase, glutamate oxaloacetate transaminase, and glutamate pyruvate transaminase. Hydrogen-reduced deazaflavin-factor 420 or flavin mononucleotide but not NAD, NADP, or ferredoxin was used as the electron donor for glutamate synthase in M. barkeri. Glutamate dehydrogenase activity was not detected in either organism, but alanine dehydrogenase activity was present in M. thermoautotrophicum. The in vivo activity of the glutamine synthetase was verified in M. thermoautotrophicum by analysis of 13NH3 incorporation into glutamine, glutamate, and alanine. Alanine dehydrogenase and glutamine synthetase activity varied in response to [NH4+] when M. thermoautotrophicum was cultured in a chemostat with cysteine as the sulfur source. Alanine dehydrogenase activity and growth yield (grams of cells/mole of methane) were highest when the organism was cultured with excess ammonia, whereas growth yield was lower and glutamine synthetase was maximal when ammonia was limiting.
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PMID:Ammonia assimilation and synthesis of alanine, aspartate, and glutamate in Methanosarcina barkeri and Methanobacterium thermoautotrophicum. 612 78

Two key steroidogenic mitochondrial cytochromes P-450 (cholesterol side-chain cleavage (scc) and 11 beta-hydroxylation (11 beta)) were purified from bovine adrenal cortex and examined as potential phosphorylatable substrates using purified cAMP-dependent protein kinase subunit (C) and A type (CKA) and G type (CKG) cAMP-independent casein kinases. Of the two cytochromes P-450, only P-450 11 beta was able to incorporate phosphate from ATP in the presence of C (Km = 7.5 microM), whereas CKA and CKG were ineffective. Phosphorylation of P-450 11 beta (maximum incorporation of 1 mole of 32P per mole of cytochrome, only on serine residues) did not modify the enzymatic activity of an 11 beta-hydroxylation system reconstituted in vitro from purified components, when adrenodoxin was in excess in the reaction. However, kinetic studies showed that P-450 11 beta phosphorylation strikingly increases the P-450 11 beta-adrenodoxin affinity in a phosphorylation-dependent manner. This would result in a net increase in 11 beta-hydroxylase activity under in vivo conditions where adrenodoxin availability is limited. Possible significance of these observations in the regulation of differentiated adrenocortical functions remains to be further examined.
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PMID:Phosphorylation of purified mitochondrial cytochromes P-450 (cholesterol desmolase and 11 beta-hydroxylase) from bovine adrenal cortex. 628 91

Diethyl pyrocarbonate inhibited diaphorase activity of ferredoxin-NADP+ oxidoreductase with a second-order rate constant of 2 mM-1 X min-1 at pH 7.0 and 20 degrees C, showing a concomitant increase in absorbance at 242 nm due to formation of carbethoxyhistidyl derivatives. Activity could be restored by hydroxylamine, and the pH curve of inactivation indicated the involvement of a residue having a pKa of 6.8. Derivatization of tyrosyl residues was also evident, although with no effect on the diaphorase activity. Both NADP+ and NADPH protected the enzyme against inactivation, suggesting that the modification occurred at or near the nucleotide binding domain. The reductase lost all of its diaphorase activity after about two histidine residues had been blocked by the reagent. In differential-labeling experiments with NADP+ as protective agent, it was shown that diaphorase inactivation resulted from blocking of only one histidyl residue per mole of enzyme. Modified reductase did not bind pyridine nucleotides. Modification of the flavoprotein in the presence of NADP+, i.e., with full preservation of diaphorase activity, resulted in a significant impairment of cytochrome c reductase activity, with a second-order rate constant for inactivation of about 0.5 mM-1 X min-1. Reversal by hydroxylamine and spectroscopic data indicated that this second residue was also a histidine. Ferredoxin afforded only slight protection against this inhibition. Conversely, carbethoxylation of the enzyme did not affect complex formation with the ferrosulfoprotein. Redox titration of the modified reductase with NADPH and with reduced ferredoxin suggested that the second histidine might be located in the electron pathway between FAD and ferredoxin.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Essential histidyl residues of ferredoxin-NADP+ oxidoreductase revealed by diethyl pyrocarbonate inactivation. 668 70

The regulation by the cell of subcellular membrane components is dependent on a highly complex balance of nutritional, hormonal and metabolic events. We have characterized the lipid components of the endoplasmic reticulum (ER) of the liver of adrenalectomized (ADX) rats and the response of these membrane components to glucocorticoid administration. Membrane microviscosity as measured by fluorescence depolarization of 1,6-diphenylhexatriene (DPH) was measured and correlated with lipid composition and content of the membranes. In the ADX rat, a significant increase in membrane microviscosity of the smooth endoplasmic reticulum (SER) was observed and this was accompanied by an increase in the cholesterol content/mg protein and a decrease in the phospholipid content/mg protein. A change in the fatty acyl chain composition is observed with a significant increase in the mole percentage of arachidonic acid (20:4) and an accompanying decrease in saturated fatty acids. Within 2-6 hr of dexamethasone administration, a decrease in membrane microviscosity is observed that returns this value to one similar to that for normal control animals. Both the cholesterol and the phospholipid contents/mg protein are likewise restored to levels similar to that for control animals beginning at the 2-hr time point. The arachidonic acid and saturated fatty acid content of the constituent phospholipids do not begin to return to values similar to those for control animals until 6 hr after dexamethasone administration. From these experiments, we can conclude that glucocorticoids play a significant regulatory role in determining the lipid properties of rat hepatic microsomal membranes.
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PMID:Dynamic lipid changes in rapidly proliferating hepatic smooth endoplasmic reticulum during acute dexamethasone treatment of adrenalectomized rats. 721 73


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