Immunochemical studies of human prolidase with monoclonal and polyclonal antibodies: absence of the subunit of prolidase in erythrocytes from a patient with prolidase deficiency.

Prolidase was highly purified from human liver and erythrocytes. NaDodSO4/acrylamide gel electrophoresis revealed that these preparations contained a major protein with MW = 56,000. The mass of prolidase was estimated on gel filtration to be MW = 97,000, for both enzyme preparations. A monoclonal antibody was raised against the liver enzyme and a specific antiserum against the erythrocyte enzyme. The monoclonal antibody (EP-2) recognized prolidase from erythrocytes and liver, in equal proportions. The antiserum also recognized the enzyme from erythrocytes and liver. Immunoprecipitation studies with these antibodies suggested only a single species of prolidase in erythrocytes and liver. Using an immobilized monoclonal antibody (EP-2) as an immunoadsorbent, prolidase was partially purified from crude extracts, and the protein of the partially purified enzyme was identified by immunoblotting using antiserum. A protein band with a MW = 56,000 was demonstrated specifically when crude extracts from the liver and erythrocytes were examined using NaDodSO4/acrylamide gel electrophoresis. The subunit protein was absent in erythrocytes from a patient with prolidase deficiency. We propose that the absence of the subunit is one cause of the prolidase deficiency.