3j8-Hydroxysteroid dehydrogenase

Key to reactions (enzymes) 0, via mevalonate, isopentenyl phosphate, squalene 1, hydroxylase, desmolase (20,22) S, A -3j8-hydroxysteroid dehydrogenase, 5(4)-isomerase S, 21-hydroxylase 4, 17a-hydroxylase 6, ll 3-hydroxylase 6, desmolase (17,20) 7, 17 -hydroxysteroid dehydrogenase 8, 19-hydroxylase 9, aromatization. 

The commonest enzymatic deficiency is a relatively severe or total absence of steroid 21-hydroxylase, but minor or severe deficiencies in the 11 -hydroxylase, and in A -3j8-hydroxysteroid dehydrogenase also occur. As with any metabolic defect of this sort, products of the reactions prior to the deficient step reach abnormally high steady-state concentrations, and their conversion by side branches of the main biosynthetic pathway to usually minor or trace metabolites may become spectacularly prominent. 

The next major step in the transformation of cholesterol to cholic acid is the conversion of the 5-choles-tene-3j8, 7a-diol into 7a-hydroxy-4-cholestene-3-one. Such conversion may occur through at least two different pathways. In the first, the substrate (5-choles-tene-3j8, 7a-diol) is sequentially attacked by a microsomal 3j8-hydroxysteroid dehydrogenase and then... 

Delta -3j8-hydroxysteroid dehydrogenase-isomerase (Ford and Engel, 1974)... 

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