Biosynthesis of Bacteriochlorophylls in Purple Bacteria

Abstract

The purple bacteria make bacteriochlorophylls for the photosynthetic mode of growth. These pigments are made from the simple precursors glycine and succinyl CoA and the initial steps in the pathway of bacteriochlorophyll biosynthesis are shared with the vitamin B12 and heme biosynthetic pathways. This chapter concentrates on the biochemical properties of the enzymes involved in each step of the pathway and the discovery and assignment of the genes encoding these enzymes. The characterization of purple bacterial enzymes involved in these steps has been crucial in understanding similar enzymes from other sources. The characterization of the early steps in the pathway within purple bacteria, such as $δ$-aminolevulinate synthase, contributed significantly to the understanding of the mammalian enzymes in the 1950s and 1960s. More recently the study of the purple bacterial enzymes toward the end of the pathway has been instrumental in identifying and characterizing the orthologous enzymes from cyanobacteria and plants. In this review we present the details of the properties of these enzymes from the purple bacteria, such as purification methods and kinetic analyses from the early literature, through to more recent studies using recombinant purple bacterial enzymes.