Rat Steroid 5α-Reductase Kinetic Characteristics: Extreme pH-Dependency of the Type II Isozyme in Prostate and Epididymis Homogenates

August 1995 in “ The Journal of Steroid Biochemistry and Molecular Biology ”

Paul N. Span, A. G. H. Smals, Fred C.G.J. Sweep, Th. J. Benraad

steroid 5α-reductase type II isozyme prostate epididymis enzyme activity pH-dependency

Studysummary This study found that the pH dependency of rat steroid 5α-reductase type II isozyme significantly affects its kinetic properties, including Vmax and Km, suggesting past discrepancies in literature may arise from these pH variances during assays.

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In the 1995 study, researchers found that the activity of rat steroid 5α-reductase type II isozyme in prostate and epididymis homogenates was highly pH-dependent. The optimal pH for the enzyme varied with substrate concentration, with pH 5.0 being optimal at high substrate concentrations and pH 5.5 at lower concentrations. The maximum efficiency (Vmax/Km) occurred at pH 5.5 for both tissues. The study highlighted that the enzyme's activity is non-linear at acidic pH unless the homogenate is pre-adjusted to the desired pH, and that the discrepancies in literature regarding 5α-reductase characteristics could be due to variations in pH during assays. The extreme pH-dependency of the type II isozyme's kinetic characteristics could explain the variations in reported enzyme activity.

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