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Properties of Lipoamide Dehydrogenase and Thioredoxin Reductase from Escherichia coli Altered by Site‐Directed Mutagenesis a
Author(s) -
WILLIAMS CHARLES H.,
ALLISON NIGEL,
RUSSELL GEORGE C.,
PRONGAY ANDREW J.,
ARSCOTT L. DAVID,
DATTA SHOMPA,
SAHLMAN LENA,
GUEST JOHN R.
Publication year - 1989
Publication title -
annals of the new york academy of sciences
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.712
H-Index - 248
eISSN - 1749-6632
pISSN - 0077-8923
DOI - 10.1111/j.1749-6632.1989.tb14986.x
Subject(s) - library science , medicine , chemistry , computer science
Lipoamide dehydrogenase and thioredoxin reductase are members of the pyridine nucleotidedisulfide oxidoreductase family of flavoenzymes, which is distinguished by an oxidation-reduction-active disulfide.’ Other members of the family, glutathione reductase and mercuric reductase, are homologous with lipoamide dehydrogenase in all domains.”5 Thioredoxin reductase is homologous with the others only in its two adenosine binding regions; the remainder of the protein, including its active-site disulfide region, appears to have evolved convergently.6 Catalysis takes place in two half-reactions, as shown in FIGURE I for lipoamide dehydrogenase.’” In the first, dithiol-disulfide interchange effects reduction of the oxidized enzyme (E) to the 2-electron reduced form of the enzyme (EH,); and in the second, the reoxidation of EH, to E, electrons pass very rapidly via the FAD to NAD’. The distinct roles of the two nascent thiols of EH, have been demonstrated.’”” The thiol nearer the amino terminus reacts almost exclusively with iodoacetamide, and it is this thiol that interchanges with the dithiol substrate; the sulfur nearer the carboxyl terminus interacts with the FAD. Similar results are seen with glutathione reductase” and mercuric reductase.” The assignment of roles to the two nascent thiols in