Comparative physical, kinetic and immunologic properties of the acidic and neutral alpha-D-mannosidase isozymes from human liver.

Human alpha-mannosidases A, B and C were partially purified from liver by conventional and affinity chromatographic procedures. The kinetic, physical and immunologic properties of the A, B and C isozymes were determined including pH optima, Km, effects of various inhibitors and activators, thermal stabilities, electrophoretic mobilities, native molecular weights and antigenic relationships. By gel filtration, the apparent native molecular weights were 240,000, 300,000 and 420,000 for the A, B and C isozymes, respectively. By polyacrylamide gel electrophoresis, the A and B isozymes had native molecular weights of approximately 150,000 and appeared to be charge isomers. Antibodies to the purified A and B isozymes were produced; cross-reactivity between the A and B isozymes against anti-A and anti-B immune sera were observed by double immunodiffusion and immunoprecipitation. In contrast, no reactivity of the C isozyme was detected with either immune serum. Based on these studies, models are presented for the molecular interrelationship of alpha-mannosidases A and B.