Trypsin activation of inactive renin in human plasma. An assessment of some methodological aspects

The following methodological aspects of the use of trypsin as activator of inactive renin in human plasma have been studied: a) the effect of SBTI on renin activity and angiotensin; b) the reaction velocity of trypsin on inactive renin; c) the optimum trypsin concentration; d) the ability of human plasma to neutralize exogenous trypsin. Our results show that: 1) Some commercially available SBTI may exert an angiotensinase-like effect which can be abolished by PMSF. 2) At 4 degrees C activation of inactive renin reached a maximum within the first two minutes then no further activation could be demonstrated. 3) Trypsin 2 mg/ml yielded more inactive renin than trypsin 1 or 0.5 mg/ml. A higher concentration (3 mg/ml) gave substantially equivalent activation as (with) trypsin 2 mg/ml whereas when using a still higher concentration (4 mg/ml) a degradation of the renin system components could be noted. 4) Endogenous trypsin inhibitors can eventually inactivate exogenous trypsin up to 3 mg/ml. About 20% of renin is destroyed by trypsin 4 mg/ml within 2 min at 4 degrees C while an additional 40% is lost during the incubation at 37 degrees C if no SBTI is added.