Hydroxylation of dehydroepiandrosterone in the eye lens

Hydroxylation of the steroid hormone dehydroepiandrosterone in the calf lens is inhibited by carbon monoxide and stimulated by NADPH. The enzyme concerned was found to be membrane-bound. Although the enzyme resembles the liver mono-oxygenase system in these characteristics, the presence of cytochrome P-450 in the lens could not be proved by measuring a difference spectrum with carbon monoxide, probably because the concentration of the enzyme is too low. Preparations of purified lens fiber plasma membranes also hydroxylate dehydroepiandrosterone. This indicates that the fiber plasma membranes act as supports for enzyme complexes. In this respect they resemble cytoplasmic membranes and plasma membranes derived from other tissues. Cultured lens cell contain the hydroxylating enzyme, although its activity is dependent on the culture conditions used. It is striking that in lens fibers the enzyme which seems to convert dehydroepiandrosterone specifically occurs on the plasma membranes, whereas, for instance, in liver, hemoproteins localized on the endoplasmic reticulum, exert hydroxylation activity towards a variety of steroids. This suggests some regulatory role for dehydroepiandrosterone in lens growth and metabolism.