peptides including hisglytrpsertyrglyglypheleu ; leuaspgluasnvalhisphephe ; gluarghisserilearg and phevalileglnglugluphe which show peptidase ability and have substrate specificity for at least one of the compounds h - ala - pro - pna , h - gly - pro - pna and h - arg - pro - pna are disclosed . nucleic acids , vectors , antibodies and hybridoma cells are also claimed with reference to the above sequences and their abilities .