Renin in the mouse submaxillary gland has a molecular weight of 40,000.

The availability of pure submaximillary renin, its antibody and pure specific immunoreactive Fab fragments of the antirenin molecule were used in an attempt to detect in which form renin is stored in the submaxillary gland. The proteolytic activity of serine-, metallo- and sulfhydryl enzymes during homogenisation was inhibited, but no inactive or high molecular weight form could be detected enzymatically or antigenically after gelfiltration. Nor were they demonstrable in crossed immuno-electrophoresis by using antibodies elicited against pure renin. Furthermore, pepstatin which additionally inhibits acid proteases, including a possible autoactivation of renin, and renin specific Fab fragments, were added, the latter in order to steric hinder proteolytic attack on a possible renin precursor. The renin-Fab complex was purified by precipitation with anti-Fab antibodies. No high molecular weight renin was demonstrable in SDS polyacrylamide gel electrophoresis. The only form of renin demonstrable in the submaxillary gland of mice was the fully active 40,000 dalton form. Its specific enzymatic activity was identical to that of pure submaxillary renin, being 0.4 . 10(-3) Goldblatt unit . ng-1.