Molecular form of pancreatic elastase 1 in human plasma

In order to study the molecular forms of immunoreactive pancreatic elastase 1 (IRE) in human plasma, we investigated the characteristics of proelastase 1, elastase 1, and their alpha 1-protease inhibitor (alpha 1-PI) complexes on anion-exchange (Mono Q) chromatography, gel (Superose 12) chromatography, and enzyme immunoassay systems with monoclonal antielastase 1 antibodies of different affinities for alpha 1-PI-elastase 1 and alpha 1-PI-proelastase 1 complexes. The rate of complex formation between proelastase 1 and alpha 1-PI was dependent on temperature of incubation and concentration of alpha 1-PI. At 37 degrees C, 90% of proelastase 1 was bound to alpha 1-PI during 2 h of incubation of purified human proelastase 1 with human alpha 1-PI. Similar results were also obtained by 2 h of incubation of proelastase 1 with human plasma at 37 degrees C. Therefore, under physiological conditions, neither free proelastase 1 nor elastase 1 can be detected in the human blood stream, and most IRE exists as the complex of proelastase 1 with alpha 1-PI in human plasma.