13C NMR studies of in vivo kinetic rates of metabolic processes

Abstract

13C NMR has been used to follow 13C labeling in suspensions of yeast cells, and in perfused mouse livers. Using [1- 13C]glucose and [6- 13C]glucose label scrambling can be observed to occur during yeast glycolysis, both in fructose-1,6-diphosphate, and in trehalose A quantitative analysis of the scrambling patterns allows one to obtain information about the kinetics of the aldolase/TPI triangle, and of futile cycling through PFK and through Fru-1,6-P 2,-ase. It is shown that the scrambling of the 13C label is different for aerobic and anaerobic glycolysis. This information can be used to study the effect of oxygen upon the kinetic rates of the TPI/aldolase part of the pathway. Gluconeogenesis has been studied in yeast, using [2- 13C]acetate as a substrate, and in perfused mouse liver by using [3- 13C]alanine and [2- 13C]ethanol. The appearance of the label could be followed in aminoacids, intermediates, and in the end-product of gluconeogenesis. From the labeling patterns information is obtained about the flow of the label through the various pathways. These experiments demonstrate that 13C NMR is a valuable technique to study the rate of metabolic processes in vivo.