Incubation of double labelled coproporphyrinogen with chicken red cell haemolysates, chemical and TLC fractionation of extracts.

Further evidence is presented for the enzymic conversion of protoporphyrinogen to protoporphyrin by observing the loss of 3H counts by 3H and 14C labelled coproporphyrinogen when incubated in chicken red cell haemolysates. Use was made of chemical and TLC fractionation of porphyrin extracts after incubation and a loss of half the 3H was again found. Evidence is presented for the role of harderoporphyrinogen as a natural intermediate in this conversion. The relevance of the findings in the porphyrias, and in particular variegate porphyria, is discussed. It is suggested that the enzymic process involved in the conversion of protoporphyrinogen to protoporphyrin may be deficient in variegate porphyria.