Fig. 5. Schematic representation of the experimental strategy for comparing utilization of extramitochondrial ATP by mitochondrially bound hexokinase or nonbound yeast hexokinase. (A) Mitochondrially bound hexokinase (HK) is represented at the center of the panel, with additional mitochondria, containing little or no bound hexokinase, shown in more peripheral regions. For the latter, rat brain mitochondria that had been depleted of hexokinase by treatment with glucose-6-phosphate, which causes release of the mitochondrially bound hexokinase, were used in earlier experiments. Later experiments, however, used rat liver mitochondria which, as isolated, do not contain bound hexokinase. Extramitochondrial ATP is distributed throughout the extramitochondrial space. (B) Analogous situation, but with an equivalent amount of nonmitochondrially bound yeast hexokinase (YHK) in place of the mitochondrially bound hexokinase. The basic strategy is to determine the rate of glucose phosphorylation by a fixed amount of bound or nonbound hexokinase as the rate of extramitochondrial ATP production is increased by addition of increasing numbers of mitochondria devoid of bound hexokinase. Reprinted with permission from de Cerqueira Cesar and Wilson (2002).

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