Biochemical and Immunological Studies on Two Distinct Ganglioside-Hydrolyzing Sialidases from the Particulate Fraction of Rat Brain

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Ganglioside-hydrolyzing sialidase activity was solubilized from rat brain particulate fraction by using Triton X-100 plus sodium deoxycholate. When chromatographed on AH-Sepharose 4B, the solubilized activity was resolved into two peaks, which were designated sialidases I and II in order of elution. The two sialidases were purified by using sequential chromatographies on Octyl-Sepharose CL-4B, Phenyl-Sepharose CL-4B, and Sephadex G-200. Sialidase II was purified further by Mono Q-FPLC. Overall purification was 450- and 2, 150-fold, for sialidases I and II, respectively. Purified sialidases I and II were maximally active at near pH 5.0 and exhibited M_r=70, 000 by gel filtration. Sialidase II hydrolyzed gangliosides but scarcely other substrates including 4-methylumbelliferyl-NeuAc (4MU-NeuAc). Sialidase II hydrolyzed oligosaccharides, glycoproteins, and 4MU-NeuAc although gangliosides appeared to be preferential substrates. Sialidase II cleaved GM₂ much faster than sialidase I. An antibody raised in rabbits against sialidase II reacted with only sialidase I and an antibody against sialidase II reacted with only sialidase II. A subcellular distribution study suggested sialidase I in the synaptosomal membrane and sialidase II in the synaptosomal and lysosomal membranes, and this was verified by using the above antibodies.