NADH-dependent decavanadate reductase, an alternative activity of NADP-specific isocitrate dehydrogenase protein

The well known NADP-specific isocitrate dehydrogenase (IDH) obtained from p ig heart was found to oxidize NADH with accompanying consumption of oxygen (NADH:O-2 = 1:1) in presence of polyvanadate. This activity of the soluble IDH-protein has the following features common with the previously described membrane-enzymes: heat-sensitive, active only with NADH but not NADPH, inc reased rates in acidic pH, dependence on concentrations of the enzyme, NADH , decavanadate and metavanadate (the two constituents of polyvanadate), and sensitivity to SOD and EDTA. Utilizing NADH as the electron source the IDH protein was able to reduce decavanadate but not metavanadate. This reduced form of vanadyl (V-IV) was similar in its eight-band electron spin resonan ce spectrum to vanadyl sulfate but had a 20-fold higher absorbance at its 7 00 nm peak. This decavanadate reductase activity of the protein was sensiti ve to heat and was not inhibited by SOD and EDTA. The IDH protein has the a dditional enzymic activity of NADH-dependent decavanadate reductase and is an example of 'one protein-many functions'. (C) 2000 Elsevier Science B.V. All rights reserved.