Inactive Renin — A Renin Proenzyme?

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Abstract
Renin cleaves an α-globulin substrate to produce the decapeptide angiotensin I. This is converted by other enzymes to the vasoconstrictor octapeptide angiotensin II. Renin is produced mainly by the kidney although extra-renal sources of the enzyme have been reported (1,2). Boyd (3) showed that in pig kidneys there is a slow-acting renin with a molecular weight (m.w.) of 60,000 as against 40,000 for active pig renin. After acidification, the slow-acting renin becomes more active and its m.w. is 40,000. In rabbit kidney extracts (4) there is an inactive renin of m.w. around 55,000, which, after exposure to pH 3.0, becomes active and its m.w. falls to 37,000, similar to that of active renin. Morris and Johnston (5) have reported an acid-activatable inactive renin of m.w. 44,000 in rat kidneys. In human kidney extracts an acid-activatable renin has been detected (6) and Day and Leutscher (7) and Day, Leutscher, and Gonzales (8) showed that inactive renin of m.w. 60,000 is present in some renal tumors and extracts of kidneys from diabetic patients. Eggena, Barrett, Silpipat and Sambhi (9) have shown that a high m.w. renin is present in human kidney. Slater and Haber (10) isolated a renin of m.w. 63,000 from normal human kidney. An acid-activatable renin is also present in human amniotic fluid (11) and human plasma (12,13,14).