The Biosynthesis of Hemoglobin From Iron, Protoporphyrin and Globin*†

The formation of heme in a system containing protoporphyrin, iron and a soluble preparation from avian erythrocytes has been studied by sev- eral investigators (3-6).The observations that the biosynthetic reaction is inactivated by heating at 560 C for 30 minutes, has a pH of optimal ac- tivity and stability near neutrality with a lower rate on each side of this optimum, and that the rate of heme synthesis is proportional to enzyme concentration, suggest, although admittedly do not prove, that the reaction is enzyme-dependent (4-6).The enzyme has been tentatively named "heme synthetase" (2, 5).However, since more than one enzyme may be involved in this reaction, the name "heme synthetase system" would be more appropriate until it can be shown that a single en- zyme is involved.The activity of the heme synthetase system is increased by reduced glutathione, cysteine, or other reducing agents (4-7).Inhibition with p-chloromercuriphenylsulfonate and with iodoacetamide suggests that active sulfhydryl groups are required for enzyme activity (5).Purification of the heme synthetase system and augmentation of heme synthesis by globin are de- scribed in the present studies.Although several