Comparative studies on nicotinamide nucleotide transhydrogenase from different sources

(1) Nicotinamide nucleotide transhydrogenases in submitochondrial particles from beef heart mitochondria, chromatophores from Rhodospirillum rubrum and membrane preparations from Escherichia coli and Pseudomonas aeruginosa have been compared with respect to the following properties: stereospecificity for the 4-hydrogen of NADH, reactivity with 3'-NADP, inhibition by palmityl-CoA, sensitivity tot rypsin, and effects of Ca2+ and 2'-AMP on the reaction rates. (2) Transhydrogenases from submitochondrial particles, R. rubrum chromatophores and E. coli membrane preparations have A-side stereospecificity for NADH, do not react with 3'-NADP, are inhibited by palmityl-CoA and are extremely sensitive to trypsin treatment. No effects of Ca2+ or 2'-AMP on the reaction rates were observed. In R. rubrum chromatophores trypsin-sensitive sites are present both in the soluble transhydrogenase factor and in the membrane preparation devoid of transhydrogenase factor. (3) In contrast, P. aeruginosa transhydrogenase is allosterically regulated by Ca2+ and 2'-AMP, is reactive with 3'-NADP, has B-side stereospecificity for NADH and is insensitive to palmityl-CoA or trypsin treatment. (4) It is concluded that the properties characterizing the transhydrogenase in E. coli, R. rubrum chromatophores and submitochondrial particles are closely connected with the interaction of the enzyme with an energy-conserving membrane system.