The action of calf brain sialidase on gangliosides, sialoglycoproteins and sialoglycopeptides

Characterization of fucosyl oligosaccharides associated with synaptic membrane and synaptic junctional glycoproteins

Rats were administered [3H]fucose by intracranial injection and synaptic membranes (SMs) isolated 18 h later. Oligosaccharides associated with SM glycoproteins were prepared by hydrazinolysis and analyzed by a combination of affinity chromatography on concanavalin A (Con A)-agarose, ion-exchange chromatography on DEAE-cellulose, and gel permeation chromatography. Most (94%) of the [3H]fucose-labelled oligosaccharides were present in the fraction that did not bind to Con A. Of these 41% did not bind to DEAE-cellulose, indicating the absence of negatively charged groups and the remainder were resolved into four fractions of increasing acidity. Gel permeation chromatography of the fractions from the DEAE-cellulose column suggested that the major oligosaccharides corresponded to fucosylated triantennary structures containing varying amounts of sialic acid although more highly branched structures containing peripheral branches lacking one or more sugars may also have been present. Comparison of fucosyl oligosaccharides associated with SMs prepared from 10- and 28-day-old animals indicated that although the general oligosaccharide content was similar at both ages, membranes from younger animals were characterized by an increase in the proportion of highly acidic structures. Fucosylated glycans derived from synaptic junctional (SJ) glycoproteins were also characterized by a greater percentage of highly acidic structures than SMs. The results indicate that SMs and SJs are characterized by specific complements of fucosylated glycoprotein oligosaccharides.

Internalization of exogenous gangliosides in cultured skin fibroblasts for the diagnosis of mucolipidosis IV

The internalization of exogenous mixed brain gangliosides in ML IV cultured skin fibroblasts indicated an impairment of ganglioside catabolism in these cells. Incubation of ML IV, normal and various other lysosomal storage disorders cell lines for five days with exogenous tritium labelled GM3, GD1a or GT1 gangliosides allowed accurate quantitation of the retained gangliosides. This in vitro approach provides a reliable method for the diagnosis of ML IV.

Identification of intrinsic sialidase and sialoglycoprotein substrates in rat brain synaptic junctions

Sialidase activity associated with rat brain synaptic junctions (SJ) and synaptic membranes (SM) was determined. Both fractions released sialic acid from exogenous glycopeptides and gangliosides. SJ accounted for 5-10% of the total sialidase activity recovered from SM following extraction with Triton X-100, and the specific activity of SJ sialidase was 60% of that of the parent SM fraction. Intrinsic SJ sialidase hydrolysed 12-15% of the sialic acid associated with endogenous SJ glycoproteins. Sialic acid residues associated with SJ glycoproteins were labelled with sodium borotritide and SJ proteins fractionated by affinity chromatography on concanavalin A-agarose. SJ glycoproteins that reacted with concanavalin A (con A+ glycoproteins) accounted for 25% of the total SJ [3H]sialic acid. Intrinsic SJ sialidase hydrolysed 20% of the [3H]sialic acid associated with these glycoproteins. Each molecular weight class of con A+ glycoprotein previously shown to be a specific component of the postsynaptic apparatus contained sialic acid and was acted on by intrinsic SJ sialidase.

Blocking action of intracellularly injected neuraminidase on central synapses in vivo

The effect of neuraminidase on synaptic transmission was studied at cholinergic and noncholinergic contacts in the buccal and cerebral ganglion of Ap]lysia. The amplitudes of monosynaptic unitary postsynaptic potentials generated by intracellular stimulation of identified presynaptic neurones were measured as indication for the efficacy of synaptic transmission. Neuraminidase was either intrasomatically injected into a presynaptic neurone, or the whole ganglion was incubated with the enzyme. Intrasomatic injection of the enzyme resulted in complete failure of synaptic transmission. This effect occurred independently of the transmitter used. The synaptic failure was presynaptic in origin. The biophysical characteristics of an injected neurone, particularly the amplitude and propagation of its action potential, did not appear to be affected by neuraminidase. Synaptic transmission and biophysical membrane properties were unaffected by extracellular neuraminidase. We conclude that the synaptic blockade is due to the enzyme's action inside the presynaptic nerve ending. It seems most likely that neuraminidase cleaves sialic-acid-containing-compounds associated with the nerve terminal surface membrane, probably thus causing failure of transmitter release.