Deficient 5 alpha-reductase due to mutant enzyme with reduced affinity to steroid substrate

Enzyme kinetics of 5 alpha-reductase were compared in cultured genital skin fibroblasts taken from 6 control subjects and from an affected subject with 5 alpha-reductase deficiency in whom the diagnosis was established on hormonal grounds. The Km value for testosterone in the mutant enzyme was extremely high (1,427 vs. 185-417 nmol/l in controls). in the mutant enzyme was extremely high (1,427 vs 185-417 nmol/l in controls). A A mutant but stable enzyme with reduced affinity to steroid substrate is reported.