Abstract
Carbohydrate substituents on the large peptide of the voltage-sensitive Na channel from Electrophorus electricus electroplax have been partially characterized by their sensitivity to endoglycosidases H and F, peptide: N-glycosidase F, Endo- N-acetylneuraminidase, and to neuraminidase. The results suggest the presence of at least two classes of oligosaccharides: neutral, high mannose or hybrid oligosaccharides, and acidic, complex oligosaccharides with a core-structure terminating in an unbranched homopolymer of sialosyl units in α-2,8 linkages (⪢5 tandem sialic acids). Large decreases in apparent Mr produced by sialidase treatments suggest an extended carbohydrate structure that could inhibit protein-protein interaction. Polysialic acid was formerly proposed to be a unique constituent of neural cell adhesion molecules (N-CAMs) in vertebrates. However, ratios of sialic acid to galactose reported for mammalian brain and muscle Na channels suggest they may also carry this oligosaccharide.
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