Purification and characterization of rabbit anti-mouse renin specific Fab fragments.

Antibodies, raised against pure renin from the submaxillary gland of mice, were used to obtain renin specific Fab fragments. The purification steps were DEAE-chromatography, followed by papain digestion with separation of the undigested IgG preparation from the Fab/Fc fragments on a Sephadex G-100 column. Finally the Fab fragments were subjected to affinity chromatography on a CH-Sepharose 4B column with submaxillary renin attached. The purified Fab fragments revealed only a single band in SDS-polyacrylamide gel electrophoresis and a single precipitation line in cross immunoelectrophoresis. The association constants for the reaction of renin with the purified Fab fragments compared to the divalent antibodies were of the same magnitude, 0.7 x 10(11) l/mol and 1.0 x 10(11) l/mol, respectively. Comparison of the affinity of the Fab fragments for the antigenic determinants and the enzymatic inhibition of renin were determined to be approximately the same. Thus, the pure specific immunoreactive Fab fragment of antirenin, with an inhibitor constant of 1.5 x 10(-11), is the most potent inhibitor of mouse renin, so far.