Structure of Pyridine Nucleotide Transhydrogenase from Azotobacter vinelandii



1. Pyridine nucleotide transhydrogenase of Azotobacter vinelandii purified by affinity chromatography consists of a mixture of polydisperse rods at neutral pH. No other structures are seen by electron microscopy.

2. At high pH (8.5–9.0) the rods depolymerize. Complete depolymerization can be achieved in 0.1 M Tris-Cl pH 9.0. The depolymerized enzyme has a molecular weight of 421000 (sedimentation equilibrium), its sedimentation coefficient 520,w= 15 S and its Stokes' radius Rs= 7 nm. Since gel electrophoresis in the presence of sodium dodecyl sulphate shows that transhydrogenase consists of a single polypeptide chain of molecular weight (54 ± 2) × 103 it follows that the depolymerized enzyme has an octameric quaternary structure. We propose that this octamer serves as the functional monomeric unit (‘unimer’) from which the polymeric form of transhydrogenase is constructed.

3. Gel filtration and sucrose gradient centrifugation studies of cell-free extracts from A. vinelandii show the unimer to be the predominant active species.


thionicotinamide-adenine dinucleotide, oxidised form


NAD(P)transhydrogenase or NADPH: NAD+ oxidoreductase (EC


alcohol dehydrogenase or alcohol: NAD+ oxidoreductase (EC


catalase or hydrogen-peroxide-hydrogen-peroxide oxidoreductase (EC


β-galactosidase or β-D-galactoside galactohydrolase (EC


glucose-6–phosphate dehydrogenase or D-glucose-6-phosphate: NADP+ 1-oxidoreductase (EC


isocitrate dehydrogenase (NADP+) (EC


pyruvate dehydrogenase complex or pyruvate: lipoate oxidoreductase (decarboxylating, CoA-acetylating) (EC


oxoglutarate dehydrogenase complex is 2-oxoglutarate: lipoate oxidoreductase (decarboxylating and acceptor-succinylating) (EC