Phosphorylation of prolidase increases the enzyme activity

Prolidase [EC 3.4.13.9] is a ubiquitously distributed imidodipeptidase that catalyzes the hydrolysis of C-terminal proline-containing dipeptides. The enzyme plays an important role in the recycling of proline for collagen syn thesis and cell growth. Although, the increase in the enzyme activity is co rrelated with increased rate of collagen turnover, the mechanism by which p rolidase is regulated remain largely unknown. In the present study we found that phosphorylation of fibroblast's prolidase may be an underlying mechan ism for up regulation of the enzyme activity. Supporting evidence comes fro m the following observations: (1) immunoprecipitated prolidase was detected as a phosphotyrosine protein as shown by western immunoblot analysis, (2) tyrosine kinase inhibitor - erbstatin induced (in a dose dependent manner) a decrease in prolidase activity in cultured human skin fibroblasts, (3) an ti-phosphotyrosine antibody reduced and phosphotyrosine phosphatase 1B anti body (anti-PTP 1B) increased (in a dose dependent manner) the prolidase act ivity in extract of fibroblast's homogenate, (4) decrease in prolidase acti vity from collagenase treated or serum starved fibroblasts can be partially prevented by incubating fibroblast's homogenate extract with anti-PTP 1B a ntibody. These results provide evidence that prolidase is phosphotyrosine e nzyme and suggest that the activity of prolidase may be up regulated by the enzyme phosphorylation.