O X I D A T I O N

R E D U C T I O N

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n i c o t i n a m i d e

3 a - Hydroxysteroid dehydrogenase from pseudomonas testeroni is a monomeric enzyme reported to form dimers with altered activity.

Aldehyde reductase from pig kidney

Gluthathione Reductase - maintainance of glutathione in reduced form is required for other biochemical reactions.

Oxido-reduction of protein thiols and formation of mixed dissulfides

GSSG + NADPH + H+ --> 2GSH + NADP+

(reduces glutathione disulfide to reduced glutathione)

Metabolic Function:

1) Glutathione - most abundant thiol - sulfate in cells. The nonequilibrim in cell extracts is limited by enzyme level orNADPH level. Also, GSH is used to protect red blood cell membranes against oxidative damage.

2) GSH is involved in the biosynthesis of deoxyribonucleic acid (as found in e.coli)

3) Glutathione reductase is from human erythrocytes (50,000 molecular weight), which has three structural domains corresponding to the binding of NADP and FAD

Thioredoxin reductase -- irreversible and involves reduction of

thioredoxin -S2 + NADPH + H+ ---> thioredoxin-SH2 +NADP+

Thioredoxin - S2 is a protein with a single disulfide bond with oxidation/reduction probability. At the central point of its structure are 3 parallel and 2unparallel strands of pleated sheets surrounded by 4 alpha helixes. There's a localized conformational change in Th-S2 before reduction. There's yeast, mammalian, and E.Coli thioredoxin. All of these "thioredoxin," through different to some extent, have an active center commonality:

Trp-Cys-Gly-Pro-Cys-Lys

Metabolic Functions of thioredoxin and thioredoxin reductase

Originally understood to be part of the cyclic electron transport system that is required for the enzymatic formation of deoxyribnucleic acid. Given RNADP = ribonucleotides dNDP = deoxyribnucleotides

Ribonucleotide reductase is from E. Coli is is essentially an allostericly regulated enzyme. Its function is to supply deoxyribonucleotides for DNA replication.

Thr. -SH2 reacts with ribonucleotide reductase in a "ping pong" mechanism.

More information can be found in Dehydrogenases Requiring Nicotinamide Coenzyme edited by Johnathan Jeffery.