An electron spin resonance study of liver and adrenal mixed function oxidases near the temperature of liquid helium.

Comparison of electron spin resonance signals of mitochondria, microsomes, and mitochondrial subfractions from the bovine adrenal cortex with the signals from rabbit liver microsomes have been made at temperatures near that of liquid helium. No evidence for the existence of an iron protein with g = 1.94 in liver microsomes could be obtained, whereas the presence of this component in adrenal cortical particles was confirmed. It was not possible to distinguish between the mitochondrial iron proteins of Beinert and those concerned with mixed function oxidation of steroids, and the relationship between mitochondrial electron transport and mixed function oxidation of steroids in the adrenal cortex remains uncertain.