Ganglioside patterns and the activities of glycosidases and sialidase were followed in eye and brain during embryonic development of the chicken beginning with the 5-day-old embryo. Acetone powders were used for enzyme assays. Gangliosides were isolated by Folch extraction and partition dialysis. In early embryonic brain and eye, monosialogan-glioside was predominant and disialoganglioside was a relatively minor ganglioside component. Trisialoganglioside was present in brain but not in eye. With embryonic development, the relative amounts of monosialoganglioside decreased and disialoganglioside increased until disialoganglioside became the predominant fraction in adult eye as well as brain. The latter constantly had proportionately moee trisialoganglioside then eye. Hexosaminidase activity toward p-nitro-phenyl N-acetyl-β-D-glucosaminide, and p-nitrophenyl N-ace-tyl-β-D-galactosaminide was found at all stages of development. In early embryonic brain and eye, specific activities were similar, but with development, decreased in eye and increased slightly before reaching adult level in brain. Specific activity for p-nitrophenyl N-acetyl-β-D-glucosaminide was higher than for galactosaminide. Galactosidase activity toward p-mtrophenyl β-D-galactopyranoside also could be detected at all stages. However, no glucosidase activity was demonstrable with either N-nitrophenyl β-D-glucoside or glucocerebroside as substrate. Galactosidase activity was similar for brain and eye in the early embryo and then diverged widely as the organs developed. Sialidase activity toward an endogenous substrate was found in brain at all developmental stages. Activity toward added, exogenous, ganglioside substrate became detectable in brain beginning with the 13th day. Sialidase activity was undetectable in adult or in embryonic eye.
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