The Cooperative Behavior of Krebs Tricarboxylic Acid Cycle Enzymes

Studies of enzymes in vitro are usually carried out under conditions that are quite different from the milieu in which they usually operate. These differences usually include the concentration of enzymes, substrates, effectors, and other physical differences, including volume exclusion of the protein milieu and possible interactions of sequential enzymes. Two recent technological advances, facile production of specific metabolic lesions by molecular biological techniques and metabolic studies with ¹³C NMR spectroscopy, offer a new window for the observation of enzyme action in vivo. In this article we present data concerning the activity of the Krebs TCA cycle enzymes in vivo employing these two newer technologies.