Angiotensin-converting enzyme in human prostate.

The activity of angiotensin-converting enzyme in human prostate was measured by spectrophotometric method using Hippuryl-L-histidyl-L-leucine (Hip-His-Leu) as substrate. Benign hypertrophic prostate had significantly higher concentration of angiotensin-converting enzyme (1.99 +/- 0.36 (S.E.M.) units/g of tissue, n = 13) than normal prostate (0.44 +/- 0.1 units/g of tissue, n = 5) (p less than 0.01). More than 80% of the enzyme activity occurred in soluble fraction of normal and hypertrophied prostates. Human prostatic angiotensin-converting enzyme, partially purified from benign hypertrophic prostates, had an apparent molecular weight of 290,000 and pI of 4.1. Optimum pH of the enzyme with KM value of 1.0 mmol/l was 7.8 in 0.1 mmol/l borate/sodium/carbonate buffer. The enzyme was competitively inhibited by captopril (Ki, 1.8 nmol/l).