Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: KEGG:D02011 (FAD)
 5,530 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The cDNA sequence of the flavoprotein subunit of bovine heart succinate dehydrogenase is reported. This is the first complete eukaryotic sequence of the flavoprotein subunit to be characterized, and it encodes a 665-amino acid protein that consists of a presequence and a 621-residue mature protein. The deduced bovine sequence shows homology to the corresponding peptides of prokaryotic succinate dehydrogenase and the related fumarate reductases; in particular, there is good overall homology (48%) to the flavoprotein subunit of Escherichia coli succinate dehydrogenase. The conserved sequences comprising the active site and those involved in FAD binding are also found in the bovine protein. The active site of the bovine polypeptide contains a cysteine that confers sensitivity of the enzyme to sulfhydryl reagents; this cysteine is only present in some sequences and thus provides a discriminatory biochemical marker. A putative flavoprotein subunit of human placental succinate dehydrogenase (partial sequence) that lacks this critical cysteine (Malcovati, M., Marchetti, T., Zanelli, T., and Tenchini, M. L. (1991) in Flavins and Flavoproteins 1990 (Curti, B., Ronchi, S., and Zanetti, G., eds) pp. 727-730, Walter de Gruyter & Co., Berlin) has only 16% homology to the bovine heart flavoprotein subunit. However, we show that the enzyme from human placenta is as sensitive to N-ethylmaleimide as that from bovine tissues. In addition, a transcript in human placenta and muscle hybridizes to the bovine heart flavoprotein cDNA and is the same size as that in bovine tissues.
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PMID:The sequence of the flavoprotein subunit of bovine heart succinate dehydrogenase. 137 42

A series of potentiometric titrations of xanthine oxidase have been performed at room temperature in the pH range 6.1-9.9. Reduction of the two Fe/S centers was monitored by CD, and that of the FAD and Mo center by EPR. The Fe/S centers behave as centers having a protonable group whose pKa changes with reduction state (E = -344 mV, pKo = 6.4, and pKr = 8.1 for Fe/S I; E = -249 mV, pKo = 6.4, and pKr = 8.0 for Fe/S II). The flavin and the two types of molybdenum centers show varying behavior, but, in all cases, electron addition is accompanied by protonation. The sequence for FAD is reduction, protonation, reduction, protonation with E1 = -398 mV, E2 = -240 mV, pK1 = 9.5, pK2 = 7.4. For "rapid" molybdenum, the sequence is protonation, reduction, protonation, reduction with E1 = -369 mV, E2 = -301 mV, pK1 = 7.9, pK2 = 8.4; and for slow molybdenum, protonation, reduction, protonation with E1 = 320 mV, E2 = -477 mV, pK1 = 7.5, pK2 = 9.5. Comparison to data obtained previously at cryogenic temperatures (Cammack, R., Barber, M. J., and Bray, R. C. (1976) Biochem. J. 157, 469-468 and Barber, M. J., and Seigel, L. M. (1982) in Flavins and Flavoproteins (Massey, V., and Williams, C. H., eds) pp. 796-804, Elsevier/North-Holland, New York) showed the centers to have significant temperature dependence, which calls for a re-evaluation of conclusions reached using cryogenic techniques (e.g. rapid-freeze). The optical absorbance characteristics of the enzyme were also investigated and a possible absorbance for molybdenum was suggested.
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PMID:The room temperature potentiometry of xanthine oxidase. pH-dependent redox behavior of the flavin, molybdenum, and iron-sulfur centers. 689 74