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

In the presence of phenylalanine and molecular oxygen, activated phenylalanine hydroxylase catalyzes the oxidation of tetrahydrobiopterin. The oxidation of this tetrahydropterin cofactor also proceeds if the substrate, phenylalanine, is replaced by its product, tyrosine, in the initial reaction mixture. These two reactions have been defined as coupled and uncoupled, respectively, because in the former reaction 1 mol of phenylalanine is hydroxylated for every mole of tetrahydrobiopterin oxidized, whereas in the latter reaction there is no net hydroxylation of tyrosine during the oxidation of the tetrahydropterin. During the course of the coupled oxidation of tetrahydrobiopterin, a pterin 4a-carbinolamine intermediate can be detected by ultraviolet spectroscopy (Kaufman, S. (1976) in Iron and Copper Proteins (Yasunobu, K. T., Mower, H. F., and Hayaishi, O., eds) pp. 91-102, Plenum Publishing Corp., New York). Dix and Benkovic (Dix, T. A., and Benkovic, S. J. (1985) Biochemistry 24, 5839-5846) have postulated that the formation of this intermediate only occurs when the oxidation of the tetrahydropteridine is tightly coupled to the concomitant hydroxylation of the aromatic amino acid. However, during the tyrosine-dependent uncoupled oxidation of tetrahydrobiopterin by phenylalanine hydroxylase, we have detected the formation of a spectral intermediate with ultraviolet absorbance that is essentially identical to that of the carbinolamine. Furthermore, this absorbance can be eliminated by the addition of 4a-carbinolamine dehydratase, an enzyme which catalyzes the dehydration of the 4a-carbinolamine. Quantitation of this intermediate suggests that there are two pathways for the tyrosine-dependent uncoupled oxidation of tetrahydrobiopterin by phenylalanine hydroxylase because only about 0.3 mol of the intermediate is formed per mol of the cofactor oxidized.
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PMID:Evidence for the formation of the 4a-carbinolamine during the tyrosine-dependent oxidation of tetrahydrobiopterin by rat liver phenylalanine hydroxylase. 272 90

Dissimilatory nitrite reductase was isolated from anaerobically nitrate-grown Vibrio fischeri cells and purified to electrophoretic homogeneity. The enzyme catalyzes the six-electron reduction of nitrite to ammonia. Upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis, under either nonreducing or reducing conditions, the purified nitrite reductase migrated as a single protein band of Mr 57,000. Gel filtration chromatography revealed a native molecular weight of 58,000, indicating the enzyme as isolated to be present in the monomeric form. Purified nitrite reductase exhibited typical c-type cytochrome absorption spectra with the reduced alpha-band at 552.5 nm. Heme content analysis using the purified preparation indicated the enzyme to contain 5.5 heme c groups per molecule. Iron analysis showed the presence of 5.62 g iron atoms per mole of enzyme and no nonheme irons were detected. These results clearly indicate that, similar to the dissimilatory nitrite reductases from Desulfovibrio desulfuricans, Wolinella succinogenes, and Escherichia coli, the V. fischeri nitrite reductase is a hexaheme c-type cytochrome. Amino acid composition of V. fischeri also revealed close similarities to those of the other three hexaheme nitrite reductases previously studied. Based on this information, it is concluded that the four ammonia-forming, dissimilatory nitrite reductases isolated to date represent a homologous group of proteins with the distinct property of being hexaheme c-type cytochromes.
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PMID:Purification of Vibrio fischeri nitrite reductase and its characterization as a hexaheme c-type cytochrome. 283 68

Reversible carbon monoxide binding has been used to examine the structural and functional properties of reduced Rhodospirillum molischianum cytochrome c'. The symmetrical dimer is found to bind CO in a noncooperative manner, indicating that the heme sites function independently and with identical carbon monoxide affinity. The enthalpy change of binding CO (aqueous) to R. molischianum ferrocytochrome c' is determined to be -11 kcal/mol of CO, which is comparable to the heat of CO binding to other heme proteins. A Bohr effect is observed (0.31 +/- 0.04 proton released per mole of CO bound at pH 8), and a basic group is involved which changes its pK from 8.3 to 7.8 upon ligation. The histidine axial ligand to the heme iron is suggested to be the source of the Bohr effect. Increased CO affinities were observed at high pH or at neutral pH in the presence of phosphate. These solvent-induced changes in CO affinity do not appear to be caused by changes in quaternary structure but rather are more likely brought about by localized changes in the vicinity of the solvent-exposed heme face.
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PMID:Carbon monoxide binding to Rhodospirillum molischianum ferrocytochrome c'. 299 May 47

Anaerobic cytochrome c552 was purified to electrophoretic homogeneity by ion-exchange chromatography and gel filtration from a mutant of Escherichia coli K 12 that synthesizes an increased amount of this pigment. Several molecular and enzymatic properties of the cytochrome were investigated. Its relative molecular mass was determined to be 69 000 by sodium dodecyl sulfate/polyacrylamide gel electrophoresis. It was found to be an acidic protein that existed in the monomeric form in the native state. From its heme and iron contents, it was concluded to be a hexaheme protein containing six moles of heme c/mole protein. The amino-acid composition and other properties of the purified cytochrome c552 indicated its similarity to Desulfovibrio desulfuricans hexaheme cytochrome. The cytochrome c552 showed nitrite and hydroxylamine reductase activities with benzyl viologen as an artificial electron donor. It catalyzed the reduction of nitrite to ammonia in a six-electron transfer. FMN and FAD also served as electron donors for the nitrite reduction. The apparent Michaelis constants for nitrite and hydroxylamine were 110 microM and 18 mM, respectively. The nitrite reductase activity of the cytochrome c552 was inhibited effectively by cupric ion and cyanide.
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PMID:Purification of a hexaheme cytochrome c552 from Escherichia coli K 12 and its properties as a nitrite reductase. 300 98

Reaction of the reduced (pink) form of the purple acid phosphatase from beef spleen with excess phosphate at pH 5.0, monitored by optical and low temperature EPR spectroscopy and by measurement of enzymatic activity, results in parallel loss of activity and oxidation of the iron chromophore. Colorimetric and radiochemical (32P) experiments indicate the presence of one mole of tightly bound phosphate in the oxidized (purple) form of the enzyme; this phosphate is released upon reduction. Acid hydrolysis of 32P-phosphate-containing enzyme, followed by high voltage paper electrophoresis, gave no evidence for significant amounts of acid-stable phosphoamino acids.
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PMID:The interaction of phosphate with the purple acid phosphatase from beef spleen: evidence that phosphate binding is accompanied by oxidation of the iron chromophore. 301 Sep 80

A soluble hydrogenase from the halophilic sulfate reducing bacterium Desulfovibrio salexigens, strain British Guiana (NCIB 8403) has been purified to apparent homogeneity with a final specific activity of 760 mumoles H2 evolved/min/mg (an overall 180-fold purification with 20% recovery yield). The enzyme is composed of two non-identical subunits of molecular masses 62 and 36 kDa, respectively, and contains approximately 1 Ni, 12-15 Fe and 1 Se atoms/mole. The hydrogenase shows a visible absorption spectrum typical of an iron-sulfur containing protein (A400/A280 = 0.275) and a molar absorbance of 54 mM-1cm-1 at 400 nm. In the native state (as isolated, under aerobic conditions), the enzyme is almost EPR silent at 100 K and below. However, upon reduction under H2 atmosphere a rhombic EPR signal develops at g-values 2.22, 2.16 and around 2.0, which is optimally detected at 40 K. This EPR signal is reminiscent of the nickel signal C (g-values 2.19, 2.16 and 2.02) observed in intermediate redox states of the well characterized D. gigas nickel containing hydrogenase and assigned to nickel by 61 Ni isotopic substitution (J.J.G. Moura, M. Teixeira, I. Moura, A.V. Xavier and J. Le Gall (1984), J. Mol. Cat., 23, 305-314). Upon longer incubation with H2 the "2.22" EPR signal decreases. During the course of a redox titration under H2, this EPR signal attains a maximal intensity around--380 mV. At redox states where this "2.22" signal develops (or at lower redox potentials), low temperature studies (below 10 K) reveals the presence of other EPR species with g-values at 2.23, 2.21, 2.14 with broad components at higher fields. This new signal (fast relaxing) exhibits a different microwave power dependence from that of the "2.22" signal, which readily saturates with microwave power (slow relaxing). Also at low temperature (8 K) typical reduced iron-sulfur EPR signals are concomitantly observed with gmed approximately 1.94. The catalytic properties of the enzyme were also followed by substrate isotopic exchange D2/H+ and H2 production measurements.
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PMID:Redox properties and activity studies on a nickel-containing hydrogenase isolated from a halophilic sulfate reducer Desulfovibrio salexigens. 301 50

An anaerobic procedure was developed for the purification of the flavin:NADH oxidoreductase (flavoprotein) component of methane monooxygenase to homogeneity. The molecular weight of the flavoprotein determined by gel filtration was about 40,000, and by sedimentation equilibrium analysis, about 38,000. The purified flavoprotein is a monomeric protein with a sedimentation constant (S20,W) value of about 2.1 S. The absorption spectrum of the flavoprotein has a peak at 460 nm and shoulder at 395 nm. The fluorescent excitation and emission spectra of the fluorescent component of flavoprotein had peaks at 450, 370, and 530 nm, respectively. A FAD was identified as a prosthetic group of flavoprotein by thin-layer chromatography. The flavoprotein contained about 1 mol of FAD and 2 mol each of iron and acid-labile sulfide per mole of protein. The flavoprotein was directly reduced by NADH under anaerobic conditions. The formation of neutral flavin semiquinone was detected during anaerobic titration of flavoprotein by NADH and also as a free radical signal at a g value of 2.004 by EPR spectroscopy. The iron sulfur cluster has g values of 2.04, 1.96, and 1.87, yielding a g average of 1.96, characteristic of a Fe2S2 center. Antibody prepared against the flavoprotein reacted with flavoprotein and inhibited methane monooxygenase activity.
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PMID:Methane monooxygenase: purification and properties of flavoprotein component. 302 58

The major iron-regulated protein (MIRP) was purified, from both Neisseria gonorrhoeae and N. meningitidis by selective extraction with cetyltrimethylammonium bromide followed by ion-exchange and moleculair-seive chromatography. Solutions of the purified proteins had a characteristic pink color. The overall amino acid composition of these proteins was similar, although differences were noted in the number of serine, threonine, and lysine residues. Nevertheless, the N-terminal amino acid sequence was identical through 47 residues for both the meningococcal and gonococcal MIRP. Plasma emission spectrophotometry revealed that the meningococcal 37K protein contained ca. 1 mole Fe/mole protein.
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PMID:Characterization of the major iron-regulated protein of Neisseria gonorrhoeae and Neisseria meningitidis. 313 Jul 84

Several iron-regulated proteins of Neisseria gonorrhoeae and Neisseria meningitidis have been reported. One of these, a 37,000-dalton protein is the major iron-regulated protein (MIRP) and appears to be common among all gonococcal and meningococcal isolates. This protein was purified from both N. gonorrhoeae and N. meningitidis and was found to contain approximately 1 mole of Fe /mole of protein. Sera from patients with gonococcal infections contained antibodies to the MIRP. Thus, the MIRP is expressed in vivo. The iron-binding nature of the MIRP suggests that it may have a role in iron acquisition by the pathogenic Neisseria species and, therefore, may have a function in their pathogenicity.
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PMID:A potential role for the major iron-regulated protein expressed by pathogenic Neisseria species. 314 15

The course of zinc protoporphyrin research has progressed at an increasingly rapid pace on several fronts. A variety of biochemical and clinical evidence viewed in toto now suggests that ferrochelatase catalyzes zinc protoporphyrin formation in states of relative iron-deficient erythropoiesis and in lead-inhibited iron metabolism. Furthermore, a redefinition of the relationship of zinc protoporphyrin to certain other parameters of iron status has been made based upon changes during the earliest states of iron depletion. These clinical studies show that the zinc protoporphyrin level and the ferritin level vary in concert but that changes in the percent transferrin saturation and in the hematocrit results are less consistent. Thus zinc protoporphyrin and ferritin are closely linked metabolically such that iron-deficient erythropoiesis becomes an initial manifestation of iron depletion. The measurement and expression of results as mumoles zinc protoporphyrin/mole heme have improved the quality of results, partly by the elimination of the assumed hematocrit designed into existing instruments. Other refinements in hematofluorometry technology have permitted exploration of the potentially extensive applications of zinc protoporphyrin measurements for lead surveillance and diagnosis, blood banking, pediatrics, obstetrics, sports medicine, and other clinical situations where a very sensitive, cost-effective indication of iron status is required.
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PMID:Zinc protoporphyrin. Past, present, and future. 332 39


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