Prolinase activity in prolidase-deficient fibroblasts

Summary

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 V_max 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.