title: Demonstration of 26-hydroxylation of C27-steroids in human skin fibroblasts, and a deficiency of this activity in cerebrotendinous xanthomatosis.
abstract: 26-Hydroxylation of 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha-triol and other C27-steroids was demonstrated in cultured skin fibroblasts from healthy individuals. Activities in skin fibroblasts were approximately 5-10% of those previously found in human liver homogenates, and were inhibited by CO. The apparent Km was lowest for 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha-triol (1.3 mumol/liter) and highest for 5-cholestene-3 beta, 7 alpha-diol (12 mumol/liter). The rate of 26-hydroxylation was highest with 7 alpha-hydroxy-4-cholesten-3-one. These characteristics are similar to those of hepatic mitochondrial C27-steroid 26-hydroxylase. In skin fibroblasts from three patients with cerebrotendinous xanthomatosis (CTX), 26-hydroxylation of C27-steroids proceeded at a rate of only 0.2-2.5% of healthy controls. No accumulation of endogenous 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha-triol could be demonstrated in these cells, and the lowered formation of radioactive, 26-hydroxylated products could not be explained by dilution of the labeled exogenous substrate. The present results add strong evidence to the concept that the primary metabolic defect in CTX is a deficiency of C27-steroid 26-hydroxylase.
mesh_terms: D001927:Brain Diseases / Q000201:enzymology*; D002478:Cells, Cultured; D053493:Cholestanetriol 26-Monooxygenase; D002777:Cholestanols / Q000378:metabolism; D005260:Female; D005347:Fibroblasts / Q000201:enzymology*; D006801:Humans; D006888:Hydroxycholesterols / Q000378:metabolism; D006900:Hydroxylation; D007700:Kinetics; D008297:Male; D008875:Middle Aged; D013250:Steroid Hydroxylases / Q000172:deficiency*; D013379:Substrate Specificity; D014973:Xanthomatosis / Q000201:enzymology*
chemical_list: D002777:Cholestanols; D006888:Hydroxycholesterols; C009561:3,7,12-trihydroxycoprostane; C011724:cholest-5-en-3 beta,7 alpha-diol; D013250:Steroid Hydroxylases; C506831:CYP27A1 protein, human; D053493:Cholestanetriol 26-Monooxygenase