Determination of porphobilinogen deaminase activity in human erythrocytes: pertinent factors in obtaining optimal conditions for measurements

Determination of porphobilinogen deaminase (PBGD; EC 4.3.1.8) activity in erythrocytes can contribute to the identification of patients suspected of acute intermittent porphyria. PBGD catalyses the polymerization of four molecules of porphobilinogen (PBG) to the highly unstable 1-hydroxymethylbilane. The 1-hydroxymethylbilane is transformed into uroporphyrinogen III by uroporphyrinogen III synthase. When this enzyme is inactivated, 1-hydroxymethylbilane cyclizes non-enzymatically to uroporphyrinogen I, which can be oxidized to uroporphyrin I. PBGD activity can be measured by quantitation of uroporphyrin I formed from PBG under conditions where this is the only end product. The purpose of the present study was to define the optimal conditions for quantitating PBGD activity in human erythrocytes. The preanalytical factors examined were: anticoagulants and methods for disruption of the erythrocytes. The analytical factors examined were: duration of preincubation, reaction time, reaction temperature, pH, ionic strength and conditions for the oxidation of uroporphyrinogen I to uroporphyrin I. Based on the results, we propose an optimized method for determination of PBGD activity in erythrocytes.