pH curve of G6PD Volendam. The enzymatic activity of G6PD partially purified from cultured fibroblasts of a healthy individual (□) or from the patient (▪) was measured at various pH values. Results are percentage of normal G6PD-B activity at pH 8. Each data point is the mean of 2 independent measurements performed in duplicate; the mean values of the 2 duplicates did not differ by more than 5%.