inhibition of human plasma renin activity by pepstatin pepstatin a pentapeptide isolated from streptomyces is a powerful inhibitor of several acid proteases its ability to inhibit the reninangiotensinogen reaction was studied in vitro in various human plasma a 50 inhibition of plasma renin activity was obtained with 106m pepstatin at ph 57 and 105m at ph 74 the inhibition of plasma renin activity by pepstatin was studied in hypertensive patients with various plasma renin levels the inhibitory effect could be demonstrated in patients with low normal and high renin activity at both phs the type of inhibition and the inhibitory constant were investigated by dixon plot and lineweaverburk plot in three separate experiments on both representations a competitive type of inhibition was found with an inhibitory constant of about 12 x 106m