A new proteinaceous factor participating in the rat ejaculate coagulation--identification, isolation and function.

A protein substance reacting with basic protein of rat seminal vesicle secretion, present in serum, testicular and epididymal homogenates and on unwashed spermatozoa, has been identified and isolated. The protein is partly of testicular origin, its concentration in male sera, testes and epididymides being age dependent and highest in sexually mature males. After castration, its concentration in male sera fails about 15%, to a comparable value present in female sera of the same age. The presence of this, as yet unrecognized, protein (molecular weight estimated at 163000) on epididymal spermatozoa is necessary for the in vitro coagulation of rat seminal vesicle proteins.