Purification and properties of human erythrocyte uroporphyrinogen decarboxylase: immunological demonstration of the enzyme defect in porphyria cutanea tarda.

The first complete purification of UROD from human erythrocytes and the characterization of the purified enzyme were described. A single enzyme protein catalyzes the four successive sequential decarboxylations of uroporphyrinogen to yield coproporphyrinogen. The enzyme activity is not directly inhibited by iron; however, it is subject to inhibition in liver cells by a number of chemicals, including environmental pollutants such as dioxin. Studies of erythrocyte UROD in PCT patients indicate that the group of patients now defined as having sporadic PCT may represent two different populations; i.e., those who have normal UROD, and those who have decreased UROD in erythrocytes. Genetic heterogeneity of the UROD defect in PCT is also indicated by the identification of both CRM(-) and CRM(+) mutations in this disorder.