You have a patient exhibiting severe episodes of hypoglycemia. Measurement of circulating insulin and glucagon levels indicate that they are normal and responsive to cycles of feeding and fasting. Which of the following enzyme defects would most likely explain the hypoglycemia?

Question

Quizplus · Accepted Answer

The Answer is C
EXPLANATION: The hepatic form of the glucosephosphorylating enzyme is referred to as glucokinase, which is a hexokinase isoform. Humans express 4 distinct hexokinases that exhibit different patterns of expression and kinetic activities relative to substrates and catalytic rates. Hepatic glucokinase has a K_m significantly higher than that of the hexokinase that is expressed in skeletal muscle. This prevents the liver from trapping glucose, thereby ensuring that peripheral tissues such as the brain and muscle have easy access to dietary carbohydrate. In the case of this patient, the expression of a variant glucokinase with a K_m similar to that of muscle hexokinase would result in significant trapping of glucose inside hepatocytes. The outcome would be expected to be periods of hypoglycemia as described.

You Have a Patient Exhibiting Severe Episodes of Hypoglycemia