Cowper’s Gland Secretion in Rat Semen Coagulation. I. Isolation and Amino Acid Analysis of the Seminal Vesicle Substrate

The seminal vesicle substrate coagulated by an acetone extract of Cowper’s gland secretion was isolated by chemical fractionation and DEAE-cellulose column chromatography and defined as the basic protein fraction of seminal vesicle secretion. Secretion from the coagulating gland at pH 7.2 also coagulated this basic protein fraction. Amino acid analysis of the basic protein showed that the molecule is characterized by a high lysine and glutamate content, a low tryptophan and methionine content, and by the absence of proline, hydroxyproline, and cysteine. The molecule has a total of 326 amino acid residues and a minimal molecular weight of 37,905. These data confirm previously published investigations by Mányai et al. (1965) on the amino acid composition of the basic protein extracted from the seminal vesicle secretion of the rat. An analysis of the washed coagulum formed by the acetone extract of Cowper’s gland secretion yielded an entirely similar amino acid pattern and molecular weight when the clotted protein was compared to substrate. In a series of experiments, the secretion of the coagulating gland was shown to potentiate the coagulating reaction between Cowper’s gland secretion extract and the basic substrate from the seminal vesicles. It was concluded that (a) both Cowper’s and coagulating gland secretion clot the same seminal vesicle substrate and (b) that this substrate is the basic protein fraction of seminal vesicle secretion.