Effect of heavy water (2H2O) on regulatory properties of phosphoglucose isomerase from Lactobacillus casei.

Phosphoglucose isomerase (D-glucose-6-phosphate ketolisomerase, EC 5.3.1.9) purified to homogeneity from Lactobacillus casei was used for studies on 2H2O effects. This preparation showed distinct differences in functional properties in H2O and 2H2O, respectively. Erythrose-4-phosphate which exerted sigmoidal inhibition in H2O, acted as a competitive inhibitor in 2H2O. The enzyme also showed reduced rate of fructose 6-phosphate formation in 2H2O. The enzyme was found to be dimeric in water and monomeric in 2H2O. The loss of regulatory properties of the enzyme has been correlated with disaggregation of the protein in heavy water, similar to that caused by sodium dodecyl sulphate treatment.