Studies on thioredoxin reductase from Escherichia coli B. The relation of structure and function.

摘要: Amino acid analyses on thioredoxin reductase indicate the following amino composition: Asp 65Thr43Ser26Glu60Pro17Gly3Ala58Val32Met12Ileu39Leu53Tyr16Phe18Try2Lys23His18Arg29 (total half-cys)8 (CONH2)59. The enzyme consists of two identical or very similar polypeptide chains joined by noncovalent bonds. This is indicated from experiments employing ultracentrifugation in urea guanidine hydrochloride, analysis tryptic peptide maps and quantitative determinations NH2-terminal acids. Carboxymethylation with iodoacetic under different conditions showed that each chain native contains one disulfide free sulfhydryl groups, latter buried structure. Titration NADPH anaerobic demonstrated complete reduction molecule requires four molecules NADPH. The results redox acceptors addition to flavin adenine dinucleotide. Evidence presented these are disulfides enzyme. Spectral studies titration substrate did not reveal formation a stable red 2-electron intermediate observed for other flavoproteins, lipoly dehydrogenase glutathione reductase. finding suggests catalytic mechanism lipoyl