Substrate specificity of manganese-activated prolidase in control and prolidase-deficient cultured skin fibroblasts.

Skin fibroblasts have a single enzyme, Mn2+-activated prolidase, that hydrolyses a range of amino acid-proline dipeptides. Two cases of prolidase deficiency showed a marked loss of activity against glycyl-proline irrespective of Mn2+ conditions. However, the abnormal enzyme showed only moderate reductions in activity against phenylalanyl-, alanyl-, and leucyl-proline following preincubation with Mn2+ or addition of Mn2+ with the substrate. Control prolidase was stable to prolonged preincubation with Mn2+, whereas the abnormal prolidase was progressively inactivated. The findings indicate, for at least the present two cases, that prolidase deficiency results from an altered rather than a marked reduction in the amount of normal enzyme.