Isoelectric patterns of human alpha1-antichymotrypsin (A1AChy) and A1AChy-protease complexes

When studied by thin-layer polyacrylamide gel isoelectric focusing, alpha1-antichymotrypsin (A1AChy) in human plasma presents a microheterogeneous pattern, consisting of seven bands with isoelectric points (pI) between 4.1 and 4.45. After removal of sialic acids by neuraminidase treatment, four bands are seen with a more alkaline pI (about 1.0 pH unit). Thus, the microheterogeneity of human A1AChy is due only in part to differential sialylation of the isoproteins. Incubation of A1AChy (in excess) with alpha-chymotrypsin results in the formation of a primary complex. In the presence of excess protease, incubation results in a secondary complex with a lower pI. Upon incubation of A1AChy with trypsin, no protease-inhibitor complexes are observed, although there is evidence for partial degradation of the A1AChy molecule.