Putting plant hexokinases in their proper place.

Hexokinases (HXKs), catalysts of the first essential step in glucose metabolism, have emerged as important enzymes that mediate sugar sensing in many organisms, including plants. The presence of several types of plant HXK isozymes, located in different intracellular locations, has been suggested. However, recent studies have indicated that most plants have only two types of HXKs, a plastidic stromal isozyme and membrane-associated isozymes located mainly adjacent to the mitochondria, but also in the nucleus. The membrane-associated isozymes are involved in sugar sensing and regulate gene expression. The central role of HXKs in plant development and the increasing interest in their role necessitate the correction of inaccuracies that have spread concerning the substrate specificity and intracellular localization of HXK isozymes, as these inaccuracies are affecting the hypothesized roles presented for these isozymes and shaping future research in this active field.