Studies on Renin with Synthetic Substrates

Renin has been shown to catalyze the hydrolysis of the protected octapeptide, Z‐Pro‐Phe‐His‐Leu‐Leu‐Val‐Tyr‐Ser‐β‐naphthylamide, at the leucyl‐leucyl bond. When the octapeptide substrate is incubated with renin and an excess of the auxiliary enzyme, aminopeptidase M, the fluorescent β‐naphthylamine is liberated at a rate related to renin concentration. A chemical assay of renin based on these facts is described in detail. When assayed with this method, kidney renin from man and pig shows pH optima of 5.4 and 5.7 respectively. Renin from submaxillary glands of mice, which also attacks the substrate, is optimally active at pH 5.4. The limit of sensitivity of the assay is 0.001 Goldblatt units for human renin and 0.01 Goldblatt units for pig renin. Trials with other possible synthetic substrates showed that Z‐Pro‐Phe‐His‐Leu‐Leu‐β‐naphthylamide is poorly hydrolyzed by renin, and Z‐Leu‐Leu‐β‐naphthylamide not at all.