Fig. 6. Rate of glucose (Glc) phosphorylation by mitochondrially bound and nonbound hexokinase, with increasing rates of ATP production from oxidative phosphorylation. The rate of Glc phosphorylation () is expressed relative to the maximal rate of phosphorylation (), the latter determined with saturating levels of exogenous ATP in the absence of oxidative phosphorylation. The rate of Glc-6-P production by nonmitochondrially bound yeast hexokinase (circles) is closely correlated with the rate of ATP production. In contrast, the rate of Glc phosphorylation by mitochondrially bound hexokinase (squares) is insensitive to increasing levels of extramitochondrial ATP produced by non-hexokinase-bearing mitochondria, consistent with the view that the mitochondrially bound enzyme is restricted to intramitochondrial ATP, produced by the mitochondria to which the enzyme is bound, as substrate. Reprinted with permission from de Cerqueira Cesar and Wilson (1998).