Properties and structural consideration of hemin a.

The mechanism by which the terminal respiratory enzyme, cytochrome oxidase, reduces molecular oxygen is still a matter of speculation. Fundamental to an understanding of this chemical mechanism is a clarification of the structure of the prosthetic group of this enzyme. Extensive work by many investigators (l-5) has clearly established that this prosthetic group is an iron porphyrin compound. This iron-containing tetrapyrrole has been labeled “hemin a” or “cytohemin.” Attempts to establish the structure of hemin a have been hampered by relatively poor isolation procedures which have resulted in material of doubtful purity. The studies of Falk and Rimington (6) have pointed out the great lability of the compounds involved. Improved techniques for the isolation and purification of hemin a (5, 7-Q) and the development of paper chromatographic techniques (8) have made possible more definitive studies of the properties of hemin a. This paper will report studies on the infrared spectra and reactions of the functional groups of hemin a, providing new information on the structure of this compound.