A Comparative Study of Porphyrin Biosynthesis

LTHOUGH the primary precursors, the intermediates and most of the enzymes involved ir the biosynthetic chain of porphyrins are now known,’,2’3 knowledge of the tissue sites( s) of porphyrin formation is incomplete. Several earlier studies4’5 demonstrated that avian nucleated erythrocytes as well as rabbit bone marrow are active in this respect. Both tissues utilize either glycine and acetate ( or succinate) or delta-aminolevulinic acid ( ALA) as precursors. However, other heme proteins are found in other tissues, as myoglobin of muscle, catalase of liver, and the cytochromes of all cells. The purpose of the present investigation was to compare the overall abilities of different tissues to synthesize porphyrinogens-porphyrins in vitro from the precursors, glycine and acetate ( or succinate ) , or ALA. Any ir crease in the amount of porphyrinogens-porphyrins in the tissue over that initially present ( “preformed” ) was interpreted as representing that synthesized from the precursor employed. Homogenates of certain canine and human tissues and “acetone powders” prepared from tissues of several species were used as the biosynthetic systems. Evidence is presented in this paper that of the tissues studied, only nucleated erythrocytes synthesize determinable amounts of porphyrins from glycine and acetate or succinate, whereas other tissues utilize ALA as a precursor but to varying degrees.