Specific basic proteins from mammalian testes. Isolation and properties of small basic proteins from rat testes and epididymal spermatozoa.

A unique acid-soluble basic protein was detected in the testes of sexually mature rats and a number of other mammalian species. This protein was not found in comparable acid extracts prepared from many other rat organs or from the testes of juvenile rats. It makes its appearance only after spermatids are evident in normally developing testes and is absent from the gonads of male rats rendered artificially cryptorchid for periods of 10 days or longer. This protein was purifled extensively and was found to be devoid of phenylalanine, tryptophan, glutamic acid, glutamine, isoleucine, and cyst(e)ine. The specific basic protein from rat testes could not be extracted from epididymal sperm by a variety of procedures. In contrast, certain techniques reproducibly extracted from both epididymal spermatozoa and whole testis a highly basic protein fraction that is strikingly rich both in arginine and cyst(e)ine.