THE PORPHYRIN REQUIREMENTS OF HAEMOPHILUS INFLUENZAE AND SOME FUNCTIONS OF THE VINYL AND PROPIONIC ACID SIDE CHAINS OF HEME* BY S. GRANICK Am) H. GILDER

Proteins bearing the prosthetic group Fe protoporphyrin IX (or closely related groups) are now recognized to function in the transport of oxygen, in the catalytic activation of O~ and H~O~, and in the shuttling of electrons from dehydrogenases tQ the oxygen-activating enzymes. The structure of this prosthetic compound is a complex one. Attention in the past has been focused mainly on the important problem of the attachment of the iron of this compound to some specific group of an apoprotein which endows the complex with its own particular activities. In this paper we shall be concerned primarily with another aspect of the Fe porphyrin ring, namely, its specific side .chains and their possible functions. The structure of Fe protoporphyrin IX (Fig. I) is well established. It consists of 4 pyrrole rings attached to each other through 4 CH-methene bridges to form a 16-membered resonating ring. In the/3 3'positions of the pyrrole rings are side chains which characterize the porphyrin type. The naturally occurring protoporphyrin IX has the following order and kinds of side chains around the ring: methyl, vinyl, methyl, vinyl, methyl, propionic acid, propionic acid, methyl. A survey of all of the structures of the known, naturally occurring Fe porphyrins, including cytochrome C, reveals that all of them, without exception, possess two propionic acid side chains in adjacent positions. Likewise the methyl side chains are a constant feature in all of them. The vinyl side chains show less constancy;here a formyl group may replace one of the vinyl groups, as in Spirographis heme; or the vinyl groups may be modified as in cytochrome C.