Immunoreactivity of proteolytic degradation products of human prostatic acid phosphatase

Prostatic acid phosphatase (EC 3.1.3.2) was fragmented by trypsin and papain in the presence of sodium dodecyl sulphate. Trypsin-catalysed cleavage gave a peptide of 33 kDa which was subsequently trimmed to 18 kDa, 15 kDa and 13 kDa peptides. Even the small tryptic fragments reacted with antiphosphatase antibodies from rabbit serum and with monoclonal antibody mAb-14. Papain treatment under these conditions resulted in the release of a 40 kDa peptide which was gradually reduced to a 18 kDa peptide. The monoclonal antibody mAb-14 to the prostatic phosphatase was bound exclusively to the 50 kDa subunit of the phosphatase and to the 40 kDa peptide. The results suggest that the monoclonal antibody mAb-14 binding site represents a "local" sequence rather than a "conformational" one and does not require an extensive tertiary folding of the antigen molecule.