Cytosolic sialidases of rat tissues with special reference to skeletal muscle enzyme

Using 4-methylumbelliferyl-N-acetylneuraminic acid as substrate, the cytosolic fractions of various rat tissues were assayed for sialidase activity. The activity was about 16 times greater in skeletal muscle than in liver, and the enzymes from the two sources were identical in chromatographic behavior, pH optimum, and substrate specificity. Apparently the same enzyme was found to be distributed in brain, heart, stomach, intestine, and testis, but not in lung and spleen. Sialidase was also present in kidney cytosol at a high level, but the enzyme resembled liver lysosomal sialidase rather than liver cytosolic sialidase in substrate specificity.