Studies on porphyrin biosynthesis in lead-intoxicated rabbits.

The present report deals with studies on porphyrins and porphyrinogen carboxy-lyase of red cells and urinary porphyrins from lead-intoxicated rabbits. It was shown that the free erythrocyte porphyrins are mixture of protoporphyrin 9, the main component, and minor proportions of Coproporphyrin, Uroporphyrin III and Phyriaporphyrin. Analysis of the urinary porphyrins deomonstrates the presence of Coproporphyrins III as the major component, together with 15-20% of other porphyrins: 10-14% 5-COOH, 1-2% 6-COOH, 2-3% 7-COOH porphyrin and 1-2% Uroporphyrin III. We have not been able to detect an increase of Uroporphyrin I. Assays of porphyrinogen carboxy-lyase activity in hemolysate supernatant using Uroporphyrinogen III and Phyriaporphyrinogen (Phyria'gen) III as substrates, showed the existence of a slight decrease of both decarboxylase activities, being more affected during the second stage, the Phyria'gen decarboxylation. A possible regulation mechanism responsible for the porphyrin picture is discussed.