Multiple molecular forms of human alanine aminopeptidase: immunochemical properties.

Human pancreas, kidney, and liver alanine aminopeptidases have similar if not identical antigenic determinants even though these three isoenzymes have distinctly different electrophoretic mobilities. Single precipitin lines without spur formation were obtained for all three enzymes with antisera obtained from rabbits immunized with these three purified enzymes. Treatment of these enzymes with neuraminidase eliminated the differences in their electrophoretic migration on polyacrylamide gels and on agarose immunoelectrophoresis gels. Treatment of the pancreas, kidney, and liver alanine aminopeptidases with their respective antibodies yielded enzymes that displayed non-competitive inhibition when the dependence of velocity upon substrate concentration was determined for each enzyme, i.e. the antibodies did not cause a change in the Km values obtained in the absence of the antibody whereas kcat was reduced to the same extent for each enzyme. The removal of sialic acid(s) from these enzymes did not alter their immunochemical characteristics or their kinetic characteristics.