Prolinase activity in prolidase-deficient fibroblasts

The activity of prolinase (EC 3.4.13.8) was studied in cultured skin fibroblasts derived from three patients with deficient prolidase (EC 3.4.13.9). With pro-val as substrate and manganese in the reaction buffer, prolinase activity was higher in prolidase-deficient cells than in control cells (mean (SEM) 917 (67) nmol min-1 mg-1, n = 3, control mean (SEM) 294, (50), n = 11). The Michaelis constants were not different for the pro-val and progly substrates in control and prolidase deficient fibroblasts. However, the constants for Vmax rose for both substrates in deficient cells. These results demonstrate that prolinase activity increases in prolidase-deficient fibroblasts as also shown in the plasma of patients with prolidase deficiency. We suggest that in prolidase-deficient fibroblasts, this rise in prolinase activity constitutes an attempt to compensate for the prolidase deficiency by increasing the greatly reduced intracellular proline pool.