Abstract
It was shown that a specific requirement for fumarate for the 11[beta]-hydroxylation of steroids arises when ox-adrenocortical mitochondria, which carry the enzymes concerned, are subjected to damaging treatment such as pre-incubation without substrate in hypo-tonic media or acetone-drying. Such enzyme preparations also require triphosphopyridine nucleotide. Satisfactory explanations of the role of triphosphopyridine nucleotide and fumarate in the 11[beta]-hydroxylation reaction cannot be offered at present.