The complex was discovered after gel filtration of the pro-apoptotic BAD protein, and contains BAD, a phosphatase, kinase, and kinase-anchoring protein directed at BAD, and glucokinase. In cells lacking BAD, the complex falls apart, respiration is compromised, and blood glucose regulation is abnormal. A nonphosphorylatable BAD leaves the complex intact but otherwise nonresponsive to glucose.
The results are consistent with a simple model: glucose induces phosphorylation of BAD, thus ensuring both cell survival and activation of glucokinase. The active glucokinase clears blood glucose and feeds the mitochondrion with necessary intermediates.
The presumption was always that the cell's two major survival pathways— glycolysis and apoptosis—were independent. But the complex hints at integration. Korsmeyer speculates that early cells may have relied on this direct integration with sugar levels, as the cells probably lacked fancy growth factors for modulating cell survival. “We could be looking at a primordial role between nutrition and cell death,” he says. “The growth factors may have come later.” This hypothesis is consistent with the ideas of Craig Thompson (University of Pennsylvania, Philadelphia, PA), who has suggested that growth factors act not directly on cell survival but via modulation of glucose levels. ▪