pH and the activity of porphobilinogen synthase in human blood

For determination of the activity of this enzyme (EC 4.2.1.24) in blood, pH dependency was evaluated by using whole blood and washed erythrocytes. The effects of assay methods, original and final pH, and use of sodium or potassium phosphate buffer were examined. The pattern of pH dependency differed for whole blood and washed erythrocytes, whether blood from normal or lead-exposed subjects was examined. The pH optimum for the activity in erythrocytes from lead-exposed subjects was the same as for the normal persons if the concentration of lead in blood did not exceed 80 microgram/100 g of whole blood. Hemolyzing blood by placing it on solid CO2 decreases the activity.