1. The precursor synthesis of renin, the storage form in the kidney and the submaxillary gland, and the molecular nature of the forms in plasma were studied in the mouse.
2. Renin is synthesized as a precursor (pre-prorenin) with a molecular weight of 50 000.
3. Renin is stored in the submaxillary gland and the kidneys as fully active renin with a molecular weight of 40 000.
4. The predominant form of renin in plasma is the active mol. wt. 40 000 form. High-molecular-weight forms of renin (800 000 and 70 000) are also present in plasma.
5. Pure 125I-labelled mol. wt. 40 000 renin binds, after a change in the tertiary structure, to the plasma protease inhibitors α2-macroglobulin, inter-α-trypsin inhibitor and α2-antithrombin. It binds also to lipoprotein and an unidentified plasma protein. No binding was seen to more than 50 other studied plasma proteins.
6. The high-molecular-weight forms of renin in plasma may be complexes of renin with plasma protease inhibitors and lipoprotein.