On the Early Evolution of Catabolic Pathways: A Comparative Genomics Approach. I. The Cases of Glucose, Ribose, and the Nucleobases Catabolic Routes.

Compared with the large corpus of published work devoted to the study of the origin and early development of anabolism, little attention has been given to the discussion of the early evolution of catabolism in spite of its significance. In the present study, we have used comparative genomics to explore the evolution and phylogenetic distribution of the enzymes that catalyze the extant catabolic pathways of the monosaccharides glucose and ribose, as well as those of the nucleobases adenine, guanine, cytosine, uracil, and thymine. Based on the oxygen dependence of the enzymes, their conservation, and evolution, we speculate on the relative antiquity of the pathways. Our results allow us to suggest which catabolic pathways and enzymes may have already been present in the last common ancestor. We conclude that the enzymatic degradations of ribose, as well as those of purines adenine and guanine, are among the most ancient catabolic pathways which can be traced by protein-based methodologies.