A high molecular weight form of angiotensin I is generated in rat serum incubated with synthetic and native angiotensin I.

Abstract

A high molecular weight form of angiotensin I, 'big angiotensin I' with m.w. 25000 was generated in rat serum incubated with angiotensin I (m.w. 1296). Angiotensin I and 'big angiotensin I' were separated by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and extracted from the gels. Only sera with high concentrations of angiotensin I (2000-4300 ng per ml) incubated at neutral pH at 24 degrees C for several hours, contained 'big angiotensin I'. 'Big angiotensin I' was stable in sera, where angiotensin I was rapidly degraded. The proportion of 'big angiotensin I' to angiotensin I in sera, where angiotensin I was stable, was approx. 5%. In addition to 'big angiotensin I', which was generated during the incubations, a serum protein with m.w. 60000 was extracted from the SDS-PAGE. This protein had angiotensin I-like activity in the radioimmunoassay, and it was isolated from the unincubated sera in concentrations at the detection limit of the radioimmunoassay.