Which of the following pairs of enzymes is required for the process of gluconeogenesis?
The three irreversible steps of glycolysis are catalyzed by hexokinase, phosphofructokinase-1 (choice B), and pyruvate kinase. In gluconeogenesis, other enzymes are needed to bypass these key steps. Pyruvate cannot be directly conveed to phosphoenolpyruvate in gluconeogenesis. Therefore, pyruvate carboxylase (a mitochondrial enzyme;) conves pyruvate to oxaloacetate, which can be conveed to phosphoenolpyruvate by phosphoenolpyruvate carboxykinase using two ATP equivalents per molecule of phosphoenolpyruvate. Fructose-1,6-bisphosphataseis the enzyme that splits fructose-1,6-bisphosphate into fructose-6-phosphate and inorganic phosphate. It is also required for gluconeogenesis. Glucose-6-phosphatase is a liver enzyme that hydrolyzes glucose-6-phosphate to glucose. A deficiency of this enzyme leads to von Gierke disease, also known as glycogen storage disease type I. Pyruvate dehydrogenase is a mitochondrial enzyme that conves pyruvate to acetyl CoA. This enzyme requires thiamine pyrophosphate, lipoamide, and FAD as cofactors. Glucokinase is a liver enzyme that conves glucose to glucose-6-phosphate. Unlike hexokinase, it is specific for glucose and is unresponsive to the level of glucose-6-phosphate. Its function is to store excess glucose, so it has a very high Km (ie, a low affinity) for glucose, becoming active only when the concentration of glucose is very high. Ref: Bender D.A., Mayes P.A. (2011). Chapter 20. Gluconeogenesis & the Control of Blood Glucose. In D.A. Bender, K.M. Botham, P.A. Weil, P.J. Kennelly, R.K. Murray, V.W. Rodwell (Eds), Harper's Illustrated Biochemistry, 29e.
Fructose-1,6-bisphosphatase and pyruvate carboxylase
Glucose-6-phosphatase and phosphofructokinase-1
Glucose-6-phosphatase and pyruvate dehydrogenase
Phosphoenolpyruvate carboxykinase and glucokinase