The activation of adrenal cortex mitochondrial malic enzyme by Ca2+ and Mg2+.
Adrenal cortex mitochondria prepared by a standard method do not exhibit malic enzyme activity. Addition of physiological concentrations of Ca2+ and Mg2+ enables these mitochondria to reduce added NADP+ by malate to form free NADPH. Half-maximum activation of the mitochondrial malic enzyme requires 0.3 mM Ca2+ and 1 mM Mg2+. Solubilized mitochondrial malic enzymes is independent of Ca2+ and has a K M of 0.2 mM for Mg2+. The Ca2+ effect is dependent on an initial period of active Ca2+ uptake which also causes other changes in respiratory properties similar to those observed with mitochondria from other tissues. After Ca2+ accumulation has taken place, free Ca2+, but not additional accumulation, is still required for malic enzyme activity. The requirement for Mg2+ can be met by Mn2+ (1 mM). This concentration of Mn2+ alone yielded only a slight activation of mitochondrial malic enzyme while higher concentrations of Mn2+ alone gave good activation of the mitochondrial malic enzy.e The NADPH generated by the Ca2+-Mg2+ activated malic enzyme effectively supports the 11beta-hydroxylation of deoxycorticosterone, whereas in the presence of malate, or malate plus Mg2+ but absence of Ca2+, the energy linked transhydrogenase supplies all the required NADPH. The activated malic enzyme appears to be more efficient than transhydrogenase in generating NADPH to support 11beta-hydroxylation. Cyanide and azide have been found to inhibit solubilized mitochondrial malic enzyme.
D000302:Adrenal Cortex / Q000187:drug effects / Q000201:enzymology*; D000311:Adrenal Glands / Q000201:enzymology*; D000818:Animals; D000963:Antimetabolites / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology*; D002417:Cattle; D004789:Enzyme Activation / Q000187:drug effects; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology*; D008291:Malate Dehydrogenase / Q000378:metabolism*; D008928:Mitochondria / Q000187:drug effects / Q000201:enzymology*
D000963:Antimetabolites; D008291:Malate Dehydrogenase; D008274:Magnesium; D002118:Calcium