Seminal pepsinogen C is not identical with, but is very similar to gastric pepsinogen C.

Human seminal pepsinogen C has been purified and compared with gastric pepsinogen C. The two zymogens cannot be distinguished by amino acid compositions and sequences of the first 28 N-terminal amino acid residues are identical. Apparent immunological identity is observed with polyclonal antisera. Monoclonal antibodies toward seminal pepsinogen C have been produced. One is able to recognize a non-carbohydrate antigenic determinant only present in seminal pepsinogen C.