An individual displays impaired glucose tolerance; blood glucose levels remain elevated after a meal for a longer time than is normal, although they do eventually go down to fasting levels. The...

An individual displays impaired glucose tolerance; blood glucose levels remain elevated after a meal for a longer time than is normal, although they do eventually go down to fasting levels. The patient has a normal release of insulin from the pancreas in response to elevated blood glucose levels. Fibroblasts obtained from the patient display normal levels of insulin binding to its receptor, and normal activation of the intrinsic tyrosine kinase activity associated with the insulin receptor. Analysis of glucose 6-phosphate formation within the fibroblasts, however, indicated a much slower rate of formation than in fibroblasts obtained from a normal control. A possible mutation that could lead to these results is which of the following?

(A) A decrease in the Km of glucokinase

(B) An increase in the Vmax of glucokinase

(C) A nonfunctional glucokinase regulatory protein

(D) An increase in hexokinase activity

(E) A decrease in hexokinase activity