Evidence for a tricarboxylic acid cycle in Serratia marcescens.

Wrede and Rothhaas (1934) proposed a tripyrrylmethene structure for the red pigment extracted from Serratia marcescens. This structure was supported by Hubbard and Rimington (1950) because of the similarity in spectral properties between extracted pigment and a synthetic tripyrrylmethene compound. Recent investigations (Williams et al., 1956) have demonstrated that pigment identical in spectral properties to that described by Hubbard and Rimington could be separated into four components. However, the pigment was still assumed to have a pyrrole nature (Green et at., 1956), and Castro et al. (1957) have reported preliminary chemical investigations which support this assumption. In addition, Santer and Vogel (1956) demonstrated that a substance presumably containing a pyrrole ring was a precursor of the pigment. Since it appears that the pigment contains pyrrole groups, one would expect that the latter substances would be synthesized by a pathway similar to that demonstrated for other forms of life. Shemin and co-workers (reviewed in Shemin, 1954-1955) have established that pyrroles are synthesized through the succinate-glycine cycle. Succinate, arising from the tricarboxylic acid cycle, condenses with glycine to form A-aminolevulinic acid, and two molecules of the latter combine to form a pyrrole. A similar mechanism has been established by investigators for the biosynthesis of pyrroles and porphyrins in microorganisms (Rimington, 1957). Hubbard and Rimington (1950) have reported that glycine and acetate are utilized for the biosynthesis of pigment by S. marcescens in a manner similar to the utilization of the compounds for the synthesis of porphyrins in other organisms. This evidence suggests that a succinate-glycine cycle operates in the production of the pigment.