Studies on the activation and molecular weight of inactive renin in human plasma

The mechanism of activation of inactive renin was studied in normal human plasma. The molecular weight of active renin and those of inactive renin before and after activation were analyzed by sephadex gel filtration. Active renin of human plasma had a molecular weight of 48,000 +/- 1000. Trypsin treatment and cold treatment activated inactive renin of a molecular weight of 54,000 +/- 1000. The inactive renin apparently did not change its molecular weight after activation. "Cryoactivation" of inactive renin was possible only when whole plasma was used. When the whole plasma was fractionated by gel filtration, cryoactivation was not observed in any of the fractions. Cryoactivation requires certain plasma factor(s) contained in some fractions. Plasma kallikrein is likely to be a major factor required for the cryoactivation of inactive renin, whereas some other factors may also participate in this mechanism.