Seminal fluid from sea urchin (Lytechinus variegatus) contains complex sulfated polysaccharides linked to protein.

The eggs of sea urchins are covered by a jelly coat, which contains high concentrations of sulfated polysaccharides. These carbohydrates show species-specificity in inducing the sperm acrosome reaction. Several studies about the egg jelly of sea urchins have been published, but there is no information about the composition of the seminal fluid of these echinoderms. Here we report for the first time the occurrence of complex sulfated polysaccharides in the seminal fluid of the sea urchin Lytechinus variegatus. These polysaccharides occur as three fractions that differ mostly in their carbohydrate/protein ratios. The native molecular masses of the polymers are very high (> or = 200 kDa) but, after digestion with papain the size decreases to approximately 8 kDa. All fractions have a similar carbohydrate composition, containing mostly galactose, glucosamine and mannose. The heterogeneous sulfated polysaccharides differ from vertebrate glycosaminoglycans and also from all previously described polysaccharides from invertebrates. The physiological role of the sulfated carbohydrates from seminal fluid is not yet determined. However, by analogy with the effects proposed for some glycoproteins found in vertebrate seminal fluid, it may be possible that the sulfated polysaccharides from invertebrate are also involved in fertilization process.