The regulation of chlorophyll and porphyrin biosynthesis

Abstract

1. 1. A fair amount of information is available on the regulation of the synthesis of porphyrin in the liver, in the chick embryo, and in Rhodopseudomonas spheroides. But little is known about the mechanism by which porphyrin synthesis is regulated in the erythropoetic system, or how both porphyrin and chlorophyll synthesis are regulated in the green plant, in Chlorella, in blue/green algae, or in animal tissues other than the liver. Porphyrin synthesis in the liver is rather special since it has to a major extent to be integrated with the biosynthesis of cytochrome P 450, a protein which is inducible by drugs and other substances, and the concentration of which varies greatly. 2. 2. In this paper we shall consider the metabolic flux of glycine and its metabolic derivative serine; the effect of haemin, the transport of glycine and aminolaevulinic acid across membranes. Special emphasis will be placed on the K m of ALA synthetase with respect to glycine, and the nature of the haemin inhibition and repression. With photosynthetic bacteria, the important case of those organisms will be discussed which can either proliferate under aerobic conditions where no bacteriochlorophyll is required, or under anaerobic conditions where large amounts of chlorophyll and also of vitamin B 12 are needed. The evidence for two forms of aminolaevulinic acid synthetase will be described, and the importance of changes in the metabolism of sulphur under different metabolic conditions, and their effect on ALA synthetase, will be considered.