MOLECULAR EVOLUTION OF PHOSPHOENOLPYRUVATE CARBOXYLASE

Phosphoenolpyruvate carboxylase is an enzyme involved in a wide variety of important metabolic pathways of plants such as anaplerotic reactions and C-4 and CAM photosynthetic pathways. The accumulation of molecular sequence data of phosphoenolpyruvate carboxylases has enabled us to investigate the function and molecular evolution of the enzymes by computer-assisted sequence comparison. Here we report the results of sequence comparison of phosphoenolpyruvate carboxylases: (1) Phosphoenolpyruvate carboxylases were classified into four groups; a subgroup of bacterial enzymes and three subgroups of plants enzymes. (2) The divergence time of the monocot enzymes involved in the C-4 pathways was roughly estimated to be 150-300 million years. On the other hand, the phylogenetic tree of the enzymes suggested that those for the dicot enzymes involved in the C-4 and CAM pathways might be close to the divergence time between the monocots and the dicots. (3) The evolutionary positions of the enzymes prevalent in roots or root nodules were identified. (4) Although sorghum and maize contained at least three genes for the enzymes in their genomes, the rates of amino acid substitution of the enzymes were different from gene to gene. The difference could not be explained by either lineage effects nor bias in base contents.