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Abstract
New polysialoglycoproteins, designated PSGP(On), were isolated from the fertilized
and unfertilized eggs of the kokanee salmon, Oncorhynchus nerka adonis. The polysialylglycan
chains consisting of alpha-2,8-linked O-acetylated poly(N-glycolylneuraminyl) chains
have recently been characterized. We have now determined the complete amino acid sequence
of the tandem-repeating units of PSGP(On) from the unfertilized eggs of kokanee salmon
and found that the following two distinct forms are present in PSGP(On) in almost
identical amounts: [formula: see text] and [formula: see text] where * denotes the
O-glycosylation site and mean value of m, n = about 20. Upon fertilization these high-molecular-weight
forms of PSGP(On) were proteolytically cleaved to the corresponding repeating units,
low-molecular-weight PSGP(On), by the action of a specific protease (PSGPase) at the
position two residues set C-terminally to the Pro residue and N-terminally to the
Asp residue, i.e. -Pro-Ser-Xaa-Asp-: [formula: see text] and [formula: see text].