The distribution and properties of transhydrogenase from animal tissues

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Abstract
Transhydrogenase occurs in animal tissues, particularly in heart muscle and to a smaller extent in skeletal muscle, kidney and liver. Other tissues such as brain, prostate, seminal vesicle, spleen and testis show small or negligible activities. Transhydrogenase is localized in mitochondria. Transhydrogenase can be purified by precipitation with ammonium sulfate in the range 20-35% saturation. Inert material are removed from solutions of transhydrogenase and the activity thus increased, by centrifuging for 3 hours at 160,000 g. The pH optimum for each of the reactions TPNH + DPN+ [forward arrow] TPN+ + DPNH and DPNH + TPN+ [forward arrow] DPN+ + TPNH is 6.3. Michaelis constants for the reaction DPNH + TPN+ [forward arrow] TPNH + DPN+ are 1.4 x 10-5 [image] DPNH and 15.7 x 10-5 [image] TPN+. The action of transhydrogenase is "strongly inhibited by sulfhydryl reagents. Solutions of transhydrogenase show maximum light absorption at 275 mu.. There is no evidence at present for the presence of any flavine or metal prosthetic group in the enzyme.