Vermorken A J, de Waal R, van de Ven W J, Bloemendal H, Henderson P T
Biochim Biophys Acta. 1977 Feb 28;496(2):495-506. doi: 10.1016/0304-4165(77)90331-2.
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.
小牛晶状体中甾体激素脱氢表雄酮的羟基化作用可被一氧化碳抑制，并被NADPH刺激。相关酶被发现是膜结合的。尽管该酶在这些特性上与肝脏单加氧酶系统相似，但通过测量一氧化碳的差光谱无法证明晶状体中细胞色素P-450的存在，这可能是因为该酶的浓度过低。纯化的晶状体纤维质膜制剂也能使脱氢表雄酮羟基化。这表明纤维质膜充当酶复合物的支撑物。在这方面，它们类似于细胞质膜和源自其他组织的质膜。培养的晶状体细胞含有羟基化酶，尽管其活性取决于所用的培养条件。引人注目的是，在晶状体纤维中，似乎能转化脱氢表雄酮的酶特别存在于质膜上，而例如在肝脏中，位于内质网上的血红素蛋白对多种甾体发挥羟基化活性。这表明脱氢表雄酮在晶状体生长和代谢中具有某种调节作用。
