The presence of multiple hexokinase isozymes (I-IV) for the phosphorylation of glucose enables specific organs to regulate carbohydrate metabolism in a unique way. Hexokinase IV, also called glucokinase, represented by the blue curve in the plot, is the predominant isozyme in liver. Hexokinase IV has distinct kinetic properties from the other hexokinase isozymes, which are represented by the red curve. Note the difference in the shapes of the curves within the physiological range of glucose concentration (~4 to 6 mM). 1 0.8 0.6 2 glucokinase (hexokinase IV) 0.4 0.2 0 + 0 2 4 6 8 10 12 14 Glucose concentration (mm) Determine whether each phrase describes glucokinase, hexokinase isozymes I-III, or all hexokinase isozymes. Note: Assume that the kinetic behavior of hexokinase isozymes in vivo is similar to in vitro. Glucokinase (hexokinase IV) Hexokinase I, II, or III All hexokinase isozymes (I-IV) Answer Bank Km is in the range of physiologic blood glucose levels subcellular localization is regulated by fructose 6-phosphate plays an important role in liver regulation of blood glucose level will be saturated by normal blood glucose concentrations when blood glucose is low, will cause cells to trap glucose by phosphorylation not sensitive to inhibition by glucose 6-phosphate will phosphorylate several hexoses including glucose when blood glucose levels fall below normal range, isozyme remains at maximum velocity