The in vitro enzymic hydroxylation of steroids. 5. Hydrogen transport in ox-adrenocortical mitochondria in relation to steroid hydroxylation

Abstract

The feeble "stimulation" of 11-deoxycorticosterone 11 B-hydroxylation in mitochondria from ox-adrenal cortex by citrate is not due to failure of this substance to enter the mitochondria or to be oxidized via isocitrate, but may be related to the fact that isocitrate oxidation which appears to be predominantly diphosphopyridine nucleotide linked in these mitochondria fails to produce adequate amounts of reduced triphosphopyridine nucleotide. The reduction of diphosphopyridine nucleotide by the mitochondria) enzymes in the presence of isocitrate, under the conditions described, cannot be attributed to the activity of a pyridine nucleotide transhydrogenase. The failure to oxidize reduced triphosphopyridine nucleotide by flavoprotein-cytochrome systems in the mitochondria and the possible significance of the transhydrogenase reaction in relation to biosynthetic reactions are discussed.