Isolation, crystallisation, and synthesis of the dimethyl ester of porphyrin a, the iron-free prosthetic group of cytochrome c oxidase

The structure of haem a, the prosthetic group of cytochrome c oxidase, has been confirmed by unambiguous synthesis of the dimethyl ester (2b) of its iron-free derivative, porphyrin a. The latter has been isolated in homogeneous state from beef heart and has been crystallised for the first time. The identity of the natural and synthetic samples of porphyrin a dimethyl ester was established by full spectroscopic and h.p.l.c. comparison. The reliability of these comparisons was strengthened by the synthesis of a closely related isomer (10a) of porphyrin a(2b) and a demonstration that the two isomers could readily be distinguished.