A highly basic small protein associated with spermatogenesis in the human testis.

A very basic and acid-soluble small protein was isolated in the pure form from specimens of human testes that displayed histologic evidence of normal spermatogenesis. The protein is virtually indistinguishable in its electrophoretic properties from a testis-specific basic protein that has been previously described in a number of other eutherian mammalian species. The homogeneous human testicular basic protein is rich in arginine, lysine, and serine, and is devoid of cyst(e)ine, phenylalanine, glutamate, glutamine, isoleucine, and tryptophan. Its amino acid composition is extremely close to that of a testis-specific basic protein previously described in the rat. The basic protein from human testis is electrophoretically distinct from the principal basic chromosomal protein of human spermatozoa and could not be detected in ejaculated human spermatozoa by the procedure used to extract the chromosomal basic protein.