SUBCELLULAR FRACTIONATION OF GANGLIOSIDE SIALIDASE FROM HUMAN BRAIN

—A subcellular fractionation was performed on forebrain cortex from three human brains and the fractions obtained were assayed for ganglioside sialidase and four p-nitrophenyl glycohydrolases. Differences in the sedimentation patterns of the enzymes were observed. From 53 to 77 per cent of the recovered sialidase activity was found in the synaptosomal fraction, while the p-nitrophenyl glycosidases were mainly recovered in the lysosome-enriched fraction. Three possible interpretations of the sialidase sedimentation pattern are suggested: (1) The ganglioside sialidase is bound to the limiting membrane structure of the nerve ending. (2) The ganglioside sialidase is lysosomal, although bound to lysosomes of low density. (3) The enzyme occurs mainly in lysosomes primarily located in the nerve endings, being trapped under the formation of the synaptosomes.