Sugars synthesized in a snap.

much higher compared to hexokinase12. Although Lau et al. have provided convincing evidence for this switching effect in cells, its effect within whole organisms is not yet known. The switching hypothesis may open a new avenue for the understanding of growth factor receptor signaling by metabolic flux by way of the hexosamine pathway. The lattice model provided by Lau et al.1 is also intriguing in that extracellular interactions can control the rate of endocytosis of cell surface receptors. Although endocytosis of receptors has been studied only with regard to cytoplasmic events such as interactions between cytoplasmic tails of receptors and adaptor proteins, this work clearly shows an extra level of control executed by the extracellular environment. Direct visualization of the lattice under several different conditions should yield fruitful indications for understanding the switch between cellular growth and arrest.