Fig. 4. Effect of adding excess unlabeled P_i on the ³²P/¹⁴C ratio of glucose-6-phosphate (Glc-6-P) formed by mitochondrially bound hexokinase or nonmitochondrially bound yeast hexokinase. Oxidative phosphorylation was initiated with ³²P_i present as substrate for oxidative phosphorylation, and [¹⁴C]Glc as substrate for hexokinase. At 3 min, excess ³¹P_i was added, reducing the specific activity of ATP subsequently produced by oxidative phosphorylation. This resulted in a precipitous decrease in the ³²P/¹⁴C ratio of Glc-6-P formed by yeast hexokinase (squares) using extramitochondrial ATP as substrate, but a much slower decrease in the ³²P/¹⁴C ratio of Glc-6-P produced by mitochondrially bound hexokinase (open circles). Filled circles, total Glc-6-P produced by mitochondrially bound hexokinase. Reprinted with permission from de Cerqueira Cesar and Wilson (1995).