The Coordination of Syntheses of Bacteriochlorophyll and Bacteriochlorophyll-Binding Proteins in Rhodobacter capsulatus

Abstract

Although bacteriochlorophyll (Bchl) synthesis has been studied for many years, very little is known about the mechanisms that coordinate the synthesis of Bchl with the availability of proteins to bind it. This is an important regulatory point, since Bchl is a potent sensitizer for photodynamic killing, but when Bchl is properly complexed with proteins and carotenoids that aid in the efficient conversion of excitation energy into electrochemical energy, Bchl can be safely accumulated to high levels. One obvious means of limiting the accumulation of free Bchl would be through feedback inhibition of Bchl synthesis, but Lascelles (1) was unable to find evidence for such a regulatory pathway. Lascelles eventually proposed that Bchl was synthesized as a Bchl-protein complex. We have recently revived that hypothesis as an explanation for the mode of regulation observed for a new Bchl-regulatory gene, pufQ (2).