13C NMR-Study of C2- and C3-Deuterated Lactic Acid Production by Parotid Cells Exposed to 13C-Labeled Glucose in the Presence of D2O

Abstract

The generation of C₂- and C₃-deuterated lactic acid produced by rat parotid cells exposed to [1-¹³C] glucose, [2-¹³C]glucose, and [6-¹³C]glucose in the presence of D₂O was assessed by ¹³C NMR, The results indicated that the escape from deuteration amounted to about 46% at the phosphoglucoisomerase level, 100% at the phosphomannoisomerase level, 65% in the reactions catalyzed by phosphofructoaldolase and triose phosphate isomerase, and 58% at the level of glutamate pyruvate transaminase. Such high values are considered to support a possible enzyme-to-enzyme tunneling of metabolic intermediates at selected sites in the glycolytic pathway.