C-13 NMR-STUDY OF C-2-DEUTERATED AND C-3-DEUTERATED LACTIC-ACID PRODUCTION BY PAROTID CELLS EXPOSED TO C-13-LABELED GLUCOSE IN THE PRESENCE OF D2O

The generation of C-2- and C-3-deuterated lactic acid produced by rat parotid cells exposed to [1-C-13] glucose, [2-C-13]glucose, and [6-C-13]glucose in the presence of D2O was assessed by C-13 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. (C) 1994 Academic Press, Inc.