Characterisation of 24-kD proteins from rat testes using polyclonal sera reactive to human sperm antigens

Abstract

A group of antigens of 24-kD Mr from rat testes were characterised biochemically. These antigens were part of a larger molecule of ∼200 kD. On treatment with disulfide bond reducing agent, the 200-kD molecule was reduced to subunits. Immunoreactivity was confined to a doublet of ∼24 kD and a single band of ∼50 kD Mr after the reduction. Glycoprotein in nature, this antigen shared immunoreactive epitopes with a 40-kD antigen on human spermatozoa. Antiserum raised in rabbits against the 24-kD antigen from rat testes reacted with antigens on the acrosome of human spermatozoa. Agglutination of sperm could be induced by the antiserum. The carbohydrate residue could be removed by mannosidase digestion. Chemical deglycosylation studies showed a slight decrease in molecular weight. Immunoreactivity was however not completely lost after chemical deglycosylation. Isoelectric focusing of the antigen identified nine isoelectric species. Two relatively minor species showed immunoreactivity. Acrosome-reacted spermatozoa showed loss of antigens from acrosome.