Presence in human cells and tissues of two prolidases and their alteration in prolidase deficiency

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Abstract
Two forms of prolidase can be separated for all the human cells and tissues examined by DEAE-cellulose column chromatography or batch methods. Serum had a very low prolidase activity eluting as a single peak prior to tissue peak I prolidase. Analysis of the two peaks can readily be carried out using white blood cells, cultured skin fibroblasts and amniotic fluid cells. Dialysis inactivated peak II prolidase although the loss can be prevented by the presence of dithiothreitol. The two peaks differed in their response to Mn2+, substrate specificity, heat stability and inhibition byp-hydroxymercuribenzoate. In two unrelated cases of prolidase deficiency, fibroblast peak I was markedly reduced, although still detectable, whereas peak II was active against all the substrates, except for a 90% reduction against glycyl-l-proline. The properties of peak II were altered in the disease. The results imply that the two forms of prolidase are structurally related.