Mutations in the phosphoglucose isomerase gene can lead to marked alterations in cellular ATP levels in cultured fibroblasts exposed to simple nutrient shifts.

The generation of ATP in a hamster fibroblast mutant devoid of the enzyme phosphoglucose isomerase (PGI) has been studied and compared with that in the parental line, which is PGI+. Both cell lines could be maintained for 24 hr in hexose media devoid of L-glutamine. Under these conditions in mannose medium, both the parental line and the PGI mutant maintained high intracellular ATP levels. With glucose under the same conditions, the parental line was able to keep the ATP level high. In contrast, the mutant line lost most of its ATP pool after incubation with glucose; the ATP/ADP ratio fell about 80% after incubation in glucose medium. Addition of pyruvate, with or without glucose, preserved the ATP pool at high levels even in the mutant, as did the presence of L-glutamine. When the PGI mutant was maintained for 3-4 days in growth medium, containing 4 mM L-glutamine and 10% dialyzed calf serum, in which glucose was replaced by mannose, the UDP-glucose pool dwindled and mediated control of the hexose uptake system did not ensue, in contrast to results of the same exposure to glucose-containing medium.