Studies on porphobilinogen deaminase and uroporphyrinogen III cosynthase from human erythrocytes

Abstract

1. 1. Porphobilinogen deaminase and uroporphyrinogen III cosynthase from human erythrocytes were isolated and partially purified. 2. 2. The deaminase had a mol.wt of 25 000 ± 5000 and behaved as a single protein. It was found to be inactivated by photooxidation and chemical oxidations, by sulphydryl reagents and by divalent metals such as Ca 2+, Cd 2+ and Mg 2+. 3. 3. The cosynthase was inhibited by sulphydryl reagents, and was not inhibited by the oxidation procedures which inhibited the deaminase. Dithiothreitol was an effective protecting agent of cosynthase. 4. 4. Deaminase and deaminase-cosynthase showed Michaelian kinetics. Uroporphyrinogen III formation increased with time and porphobilinogen concentration. 5. 5. A number of porphobilinogen analogues were examined as substrates of the system. None of them behaved as such, while several were effective inhibitors. 6. 6. Deaminase was bound to a Sepharose support and the immobilized enzyme associated with cosynthase in the absence of porphobilinogen. The whole complex formed uroporphyrinogen III.