1. The low-molecular-weight (40 000) form of renin was converted into the high-molecular-weight (60 000) form of renin with sulphydryl oxidation, and the high-molecular-weight form of renin was re-converted into the low-molecular-weight form with a reduction of disulphide bonds in the renal cortical homogenate of the dog. Therefore, the low- and high-molecular-weight forms of renin were interconvertible. 2. The formation of high-molecular-weight form of renin required a renin binding substance which was found to be included in the cytosol fraction of kidney cortex of the dog. 3. The renin binding substance of the dog was unstable to heat and low pH, but vitally resistant to Triton X-100 and chloroform. It did not bind to concanavalin A Sepharose 4B. 4. The renin binding substance was eluted in the molecular-weight region between 156 000 and 60 000 on Sephadex G-200, and such apparent molecular weight was not altered by urea at 4 mol/l; thus molecular weight greater than the theoretically expected value of 20 000 was indicated.
1. Renin release from isolated dog renin granules was limited to within 20% of the total renin during incubation at 37°C in isotonic medium and did not depend on the external concentration of renin. 2. Although the renin granules were osmotically and mechanically fragile, they were quite stable at 0°C in isotonic medium. 3. The bulk of renin activity appeared in the supernatant when the granules were ruptured by osmotic lysis. About 8% of the total renin still remained in the membrane fraction of the granules after treatment by freezing and thawing. 4. Therefore stored renin in the granules can be described as comprising three components: a readily released soluble form; a soluble but hard-to-release form; a membrane-bound form.
1. The renin inhibitory effect of 2-[4-(4′-chlorophenoxy)phenoxy - acetylamino]ethylphosphoryl - ethanolamine (PE-104) was examined both in vitro and in vivo. 2. PE-104 inhibited the rate of angiotensin formation from dog renin and renin substrate reaction. The K i value was 2 mmol/l and the inhibition was competitive. 3. In normotensive rats, infusion of PE-104 abolished the increases of blood pressure and plasma angiotensin I concentration due to renin injection. In renal hypertensive rats, infusion of PE-104 decreased blood pressure and this was associated with a decrease of plasma angiotensin I concentration. 4. These observations confirm that PE-104 is a renin inhibitor.