ACTIVATION AND INHIBITION OF MITOCHONDRIAL TRANSHYDROGENASE BY METAL-IONS

Mitochondrial transhydrogenase has been reported previously to be inhi bited by high, rather non-physiological concentrations (in the range o f 2-20 mM) of divalent cations. We show that the enzyme could be activ ated by low (from about 1 muM to 1 mM) concentrations of Ca2+ and Mg2, which are within physiological range. These results bring in line th e effects observed with mitochondrial enzyme to the findings with bact erial transhydrogenases. The activation of transhydrogenase by divalen t cations is interpreted as an increase in affinity of the NADP(H)-bin ding site of the enzyme-NAD(H) complex. Reported effects of the metal ions could be important for the enzyme function in vivo.