Secretion and glycosylation of rabbit macrophage type V collagenase

Cultures of freshly isolated rabbit alveolar macrophages were used to study the synthesis, secretion, and glycosylation of type V collagenase. Cells were pulse-labeled with [35S-]methionine for 15 minutes followed by a chase with cold methionine for various time periods. Type V collagenase was identified in the culture supernatants and cell lysates by immunoprecipitation with a specific antiserum. Within 10 minutes of chase, an 82-kDa protein was found in the cell lysates. This protein was subsequently processed to a 92-kDa protein without identifiable intermediate forms. By 60 minutes of chase, intracellular radioactivity was no longer detectable. The larger protein could be detected within 20 minutes in the culture supernatants and accumulated in the medium for 60 minutes of chase time. Only the 92-kDa form was seen in the supernatants and the proteinase was secreted without intracellular storage or membrane association. Treatment of the 92-kDa proteinase with an enzyme which specifically removes N-linked carbohydrates resulted in an apparent reduction in molecular mass of approximately 10 kDa. Deglycosylation of the proteinase did not result in an apparent loss of activity. Thus, it was concluded that macrophage type V collagenase is synthesized as an 82-kDa polypeptide which is glycosylated by N-linkage and secreted.