The major androgen-regulated secretory proteins of the rat epididymis bear sequence homology with members of the alpha 2u-globulin superfamily.

The primary amino acid sequence of 18.5 kDa androgen-dependent secretory proteins of the rat epididymis has been compared with protein data-base sequences. The comparison has revealed that the epididymal proteins belong to the alpha 2u-globulin superfamily which includes human, rat and mouse urinary proteins, ungulate beta-lactoglobulins, and serum retinol-binding proteins. The homology suggests that the epididymal proteins may function to transport retinoids within the male reproductive tract. The androgen-dependent characteristics of the proteins and their tissue-specific nature have been ascertained by use of the protein's cDNA as a probe. The mRNA for the proteins was found in the epididymis of the rat and mouse, but not the epididymis of guinea-pig, rabbit, bull, boar, or ram.