Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0016632 (Fox)
 1,461 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Trichloroethylene was oxidized by purified toluene dioxygenase obtained from recombinant E. coli strains. The major oxidation products were formic acid and glyoxylic acid. Other potential products, dichloroacetic acid, chloral, phosgene, carbon monoxide, and carbon dioxide, were not detected. [14C]trichloroethylene became covalently attached to protein components and NADPH suggesting non-specific alkylation by reactive products. Oxidation of deuterated trichloroethylene yielded 50.2% deuterated formate. Oxidation of trichloroethylene in D2O yielded 43.7% deuterated formate. These data indicate that both carbon atoms are giving rise to formic acid. The results are consistent with a mechanism of TCE oxygenation not involving epoxide, dioxetane, or dihydroxy intermediates and indicate significant differences from those previously proposed for cytochrome P-450 (Miller, R.E. & Guengerich, F.P. (1982) Biochemistry 21, 1090-1097) or methane monooxygenase (Fox, B.G., Borneman, B.G., Wackett, L.P., & Lipscomb, J.D. (1990) Biochemistry 29, 6419-6227).
 ...
PMID:Trichloroethylene oxidation by toluene dioxygenase. 159 83

NADPH-sulfite reductase flavoprotein (SiR-FP) was purified from a Salmonella typhimurium cysG strain that does not synthesize the hemoprotein component of the sulfite reductase holoenzyme. cysJ, which codes for SiR-FP, was cloned from S. typhimurium LT7 and Escherichia coli B, and both genes were sequenced. Physicochemical analyses and deduced amino acid sequences indicate that SiR-FP is an octamer of identical 66-kDa peptides and contains 4 FAD and 4 FMN per octamer. Potentiometric titrations of SiR holoenzyme, SiR-FP, and FMN-depleted SiR-FP yielded the following redox potentials for the prosthetic groups at pH 7.7: E'1 (FMNH./FMN) = -152 mV; E'2 (FMNH2/FMNH.) = -327 mV; E'3 (FADH./FAD) = -382 mV; E'4 (FADH2/FADH.) = -322 mV. Microcoulometric titration of SiR-FP at 25 degrees C yielded data which were in full agreement with these potentials. Spectroscopic and catalytic studies of native SiR-FP and of SiR-FP depleted of FMN support the following electron flow sequence: NADPH----FAD----FMN. FMN can then contribute electrons to the hemoprotein component of sulfite reductase, as well as to cytochrome c and various diaphorase acceptors. The FMN is postulated to cycle between the FMNH2 and FMNH. oxidation states during catalysis; in this sense SiR-FP shares a catalytic mechanism with NADPH-cytochrome P-450 oxidoreductase. SiR-FP domains involved in binding FMN, FAD, and NADPH are proposed from amino acid sequence homologies with Desulfovibrio vulgaris flavodoxin (Dubourdieu, M., and Fox, J.L. (1977) J. Biol. Chem. 252, 1453-1463) and spinach ferredoxin-NADP+ oxidoreductase (Karplus, P.A., Walsh, K.A., and Herriott, J. R. (1984) Biochemistry 23, 6576-6583). Comparison of the deduced amino acid sequences of SiR-FP and NADPH-cytochrome P-450 oxidoreductase (Porter, T. D., and Kasper, C.B. (1985) Proc. Natl. Acad. Sci. U. S.A. 82, 973-977) also showed identities that suggest these two proteins are descended from a common precursor, which contained binding regions for both FMN and FAD.
 ...
PMID:Characterization of the flavoprotein moieties of NADPH-sulfite reductase from Salmonella typhimurium and Escherichia coli. Physicochemical and catalytic properties, amino acid sequence deduced from DNA sequence of cysJ, and comparison with NADPH-cytochrome P-450 reductase. 255 Apr 23

Mercuric reductase contains FAD and a redox-active disulfide which is reduced to a thiol/thiolate pair in two-electron reduced enzyme (EH2) (Fox, B. and Walsh, C.T. (1982) J. Biol. Chem. 257, 2498-2503). A charge transfer interaction between the thiolate and oxidized FAD gives EH2 a characteristic absorption spectrum, very similar to that found with other flavoprotein disulfide oxidoreductases. We have examined the reaction of EH2 with HgCl2 (+/- mercaptoethanol) in stopped-flow kinetic and static titration experiments. In the absence of mercaptoethanol, reaction of EH2 with HgCl2 yields a final spectrum which is indistinguishable from that of oxidized enzyme. The nature of the final species was examined by titration of enzyme thiols with 5,5'-dithiobis-2,2'-nitrobenzoic acid under denaturing conditions in the presence of NaI to displace any Hg(II) bound to enzyme thiols. These studies demonstrate that EH2 tightly complexes Hg(II) with its active site thiols, but is incapable of reducing Hg(II) to Hg0. For the latter reaction to occur, additional reducing equivalents are required. In catalysis, the enzyme must first be reduced to EH2 after which it cycles between EH2 and EH2 X NADPH forms. This is in contrast to other flavoprotein disulfide oxidoreductases which cycle between Eox and EH2 forms in catalysis (Williams, C. H., Jr. (1976) in The Enzymes (Boyer, P. D., ed) 3rd Ed., Vol. 13, pp. 89-173, Academic Press, New York). With mercuric reductase, exogenous thiols are required for catalytic reduction of Hg(II) to Hg0. We have shown that this is due to prevention or reversal of formation of an abortive complex of Hg(II) with the thiol/thiolate pair of EH2.
 ...
PMID:Two-electron reduced mercuric reductase binds Hg(II) to the active site dithiol but does not catalyze Hg(II) reduction. 352 63

The mercuric ion reduction system encoded by the Hg2+ inducible mer operon confers bacterial resistance to mercuric ion. The mer A gene product which is a FAD-containing enzyme catalyzes the reduction of Hg2+ to volatile elemental mercury with the help of intracellular thiols and NADPH as a cofactor (Schottel 1974; Summers and Silver 1978; Fox and Walsh 1982; Misra 1992). Our earlier studies have shown that growing cells of different mercury-resistant bacteria reduce Hg2+ compounds to Hg(O) (Ray et al. 1989; Pahan et al. 1990a; Gachhui et al. 1989). We have also shown the effect of thiol compounds and flavins on mercury-degrading enzyme activities in mercury-resistant bacteria (Pahan et al. 1990b). Here we report that resting cells of mercury-resistant bacteria survive in a buffer system for several hours, synthesize inducible mercury-degrading enzymes and volatilize mercury from a mercury-containing buffer system. We know of no information regarding studies of mercury-degrading enzymes in resting mercury-resistant bacterial cells.
 ...
PMID:Volatilization of mercury by resting mercury-resistant bacterial cells. 872 98

Old Yellow Enzyme (OYE) binds phenolic ligands forming long wavelength (500-800 nm) charge-transfer complexes. The enzyme is reduced by NADPH, and oxygen, quinones, and alpha,beta-unsaturated aldehydes and ketones can act as electron acceptors to complete catalytic turnover. Solution of the crystal structure of OYE1 from brewer's bottom yeast (Fox, K. M., and Karplus, P. A. (1994) Structure 2, 1089-1105) made it possible to identify histidine 191 and asparagine 194 as amino acid residues that hydrogen-bond with the phenolic ligands, stabilizing the anionic form involved in charge-transfer interaction with the FMN prosthetic group. His-191 and Asn-194 are also predicted to interact with the nicotinamide ring of NADPH in the active site. Mutations of His-191 to Asn, Asn-194 to His, and a double mutation, H191N/N194H, were made of OYE1. It was not possible to isolate the N191H mutant enzyme, but the other two mutant forms had the expected effect on phenolic ligand binding, i.e. decreased binding affinity and decreased charge-transfer absorbance. Reduction of the H191N mutant enzyme by NADPH was similar to that of OYE1, but the reduction rate constant for NADH was greatly decreased. The double mutant enzyme had an increased rate constant for reduction by NADPH, but the reduction rate constant with NADH was lower by a factor of 15. The reactivity of OYE1 and the mutant enzymes with oxygen was similar, but the reactivity of 2-cyclohexenone was greatly decreased by the mutations. The crystal structures of the two mutant forms showed only minor changes from that of the wild type enzyme.
 ...
PMID:On the active site of Old Yellow Enzyme. Role of histidine 191 and asparagine 194. 983 19