Tetsu Shimizu, N. Takaya, A. Nakamura
Oct 4, 2012
Citations
2
Influential Citations
35
Citations
Journal
The Journal of Biological Chemistry
Abstract
Background: l-Glucose, the enantiomer of d-glucose, was believed not to be utilized by any organisms. Results: An l-glucose-utilizing bacterium was isolated, and its l-glucose catabolic pathway was identified genetically and enzymatically. Conclusion: l-Glucose was utilized via a novel pathway to pyruvate and d-glyceraldehyde 3-phosphate. Significance: This might lead to an understanding of homochirality in sugar metabolism. An l-glucose-utilizing bacterium, Paracoccus sp. 43P, was isolated from soil by enrichment cultivation in a minimal medium containing l-glucose as the sole carbon source. In cell-free extracts from this bacterium, NAD+-dependent l-glucose dehydrogenase was detected as having sole activity toward l-glucose. This enzyme, LgdA, was purified, and the lgdA gene was found to be located in a cluster of putative inositol catabolic genes. LgdA showed similar dehydrogenase activity toward scyllo- and myo-inositols. l-Gluconate dehydrogenase activity was also detected in cell-free extracts, which represents the reaction product of LgdA activity toward l-glucose. Enzyme purification and gene cloning revealed that the corresponding gene resides in a nine-gene cluster, the lgn cluster, which may participate in aldonate incorporation and assimilation. Kinetic and reaction product analysis of each gene product in the cluster indicated that they sequentially metabolize l-gluconate to glycolytic intermediates, d-glyceraldehyde-3-phosphate, and pyruvate through reactions of C-5 epimerization by dehydrogenase/reductase, dehydration, phosphorylation, and aldolase reaction, using a pathway similar to l-galactonate catabolism in Escherichia coli. Gene disruption studies indicated that the identified genes are responsible for l-glucose catabolism.