The effects of development on activity, specificity and endogenous substrates of synaptic membrane sialidase

Abstract

Synaptic plasma membranes were prepared from cortices of rats varying in post-natal age between 4 and 30 days. Sialic acid associated with synaptic plasma membrane glycoproteins and gangliosides increased 75% and 50%, respectively, between 4 and 30 days. The amount of sialic acid released from these membrane constituents by intrinsic synaptic sialidase increased 2–4-fold over the same period. Incubation of synaptic plasma membranes with exogenous gangliosides or glycopeptides demonstrated a 2–3-fold incrase in sialidase activity during development. The major gangliosides present in synaptic plasma membranes at all ages were GT 1, GD 1a, GD 1b and GM 1. Intrinsic sialidase hydrolyzed 50–70% of endogenous GT 1 and GD 1a gangliosides at all ages. Endogenous GD 1b ganglioside was poorly hydrolyzed in young rats and its susceptibility to enzymic hydrolysis increased during development. When exogenous GD 1a and GD 1b were used as substrates a preferential increase in activity against GD 1b occured during development, the ratio of activity (GD 1a/GD 1b) decreasing from 3.6 to 1.6 between 7 and 30 days. 10- and 30-day-old synaptic plasma membranes contained complex mixtures of sialoglycoproteins, an increase in the relative concentrations of lower molecular weight sialoglycoproteins occuring development. Intrinsic sialidase present in 10- and 30-day-old synaptic plasma membranes acted upon all molecular weight classes of sialoglycoproteins.