Introductory remarks

Abstract

Our present knowledge of the mode of formation in living cells of the porphyrins dates from the classic paper by Shemin & Rittenberg, who showed that the nitrogen atom of glycine was specifically used in the biosynthesis of protoporphyrin. In the following five years it was demonstrated that glycine and succinyl-coenzyme A combine under the influence of a specific enzyme, and in the presence of pyridoxal phosphate, to give 5-aminolaevulinic acid, and the carbon and nitrogen atoms of this compound account for all the carbon and nitrogen atoms in protoporphyrin. The main outlines of the reactions leading to haem are now established. We have also good reasons to believe that chlorophylls a and b and others are derived from protoporphyrin. It is also well established that the insertion of magnesium is a first step in the specific biosynthetic pathway of chlorophyll, and this insertion is followed or associated with the esterification of one of the carboxyl groups of one of the two propionic acid side-chains. Full details of these reactions and particularly the sequence of the various steps are still a matter for further investigation.