Uroporphyrinogen 3 cosynthetase in human congenital erythropoietic porphyria

Activity of the enzyme uroporphyrinogen III cosynthetase in hemolysates from five patients with congenital erythropoietic porphyria was much lower than the activity in control samples. The low cosynthetase activity in patients was not due to the presence of a free inhibitor or some competing enzymatic activity, because hemolysates from porphyric subjects did not interfere either with the cosynthetase activity of hemolysates from normal subjects or with cosynthetase prepared from hematopoietic mouse spleen. This partial deficiency of cosynthetase in congenital erythropoietic porphyria corresponds to that shown previously in the clinically similar erythropoietic porphyria of cattle and explains the overproduction of uroporphyrin I in the human disease.