Fig. 3. Glucose (Glc) phosphorylation by mitochondrially bound hexokinase, with ATP generated by oxidative phosphorylation in the presence of increasing concentrations of exogenous ATP. ATP production by oxidative phosphorylation was initiated by addition of ADP at the indicated time. Glc phosphorylation was coupled to NADPH production, monitored by absorbance at 340 nm (A), in the presence of excess glucose-6-phosphate (Glc-6-P) dehydrogenase. The concentrations of exogenous ATP, present at the time of ADP addition, were 1.1, 0.66, 0.22 and 0 mmol l^-1 for curves A–D, respectively. Note that the steady state attained was independent of the original extramitochondrial [ATP]. Reprinted with permission from BeltrandelRio and Wilson (1992b).