Relative high activity and moderate relative abundance of metabolic enzyme in central carbon metabolism suggests evolutionary hand in enzyme activity tuning

RNA-seq transcriptome analysis of many microbial cells does not yield hits involving metabolic enzymes in central carbon metabolism amongst the highest expressed genes. This suggest moderate expression level of these essential enzymes in metabolism. This bets the question of why critical enzymes are not expressed at a higher level, which may help deliver a higher growth rate and better competitiveness for nutritional sources in a microbiome community. More importantly, metabolic enzymes are essential for churning the building blocks and harvesting energy to support life, and, at the theoretical level, should have either high relative abundance or high activity to support the metabolic needs of the cell. Taking the above together, the most plausible view is that enzymes in central carbon metabolism enjoys a relatively high level of activity for them to deliver sufficient catalytic activity at moderate relative abundance level. Such a situation calls for a re-examination of our understanding of bacterial metabolism and cell biology. Specifically, the evolutionary question revolves around the trade-off between metabolic burden from high enzyme expression level for low activity enzymes, and lower burden from moderately abundant enzymes of high activity level. Hence, evolution should have welded its hand in selecting moderate expression level of high activity enzymes to afford a fitness advantage to cells through reducing the material and energy cost of expressing the enzymes. This schema requires understanding that enzymes are essential machineries in the cell that requires frequent re-transcription and translation that incurs energy and cellular building block. Overall, RNA-seq revelation of moderate expression level for metabolic enzymes in central carbon metabolism suggests evolution may have tuned the enzymes with high activity to afford a lower metabolic burden to the cell in exchange for a fitness advantage in varied environments.