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

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Abstract
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.