Amino acid sequence of beta-microseminoprotein from porcine seminal plasma.

beta-Microseminoprotein is a small mucus-associated protein of unknown function, previously characterized in man and the ape. The corresponding porcine protein was identified in tracheal mucus and seminal plasma by its cross-reaction with antibodies raised against the human protein. The porcine protein was isolated from seminal plasma, and its complete amino acid sequence determined. It is a single-chain protein of 91 amino acids with a molecular mass of 10,068 Da. Compared to primate beta-microseminoprotein, the porcine protein has a blocked N-terminus and a deletion of three amino acids in the N-terminal region, but otherwise manifests similarity in amino acid sequence including conservation of 10 cysteine residues. A proportion of individual pigs have two forms of the protein, differing in charge but not in size. The characterization of beta-microseminoprotein in a species suited for experiments should help determine the function of this protein.