Question

Synthesis of fructose-2,6-bisphosphate is catalyzed by a bifunctional enzyme that contains two catalytic domains: PFK2 (kinase domain) and FBPase2 (phosphatase domain). How is glucose metabolism affected when the PFK2/FBPase2 enzyme is phosphorylated?

		Both glycolysis and gluconeogenesis occur simultaneously
		Glycolysis is upregulated, gluconeogenesis is downregulated
		Glycolysis is downregulated, gluconeogenesis is upregulated
		Glycolysis and glycogen synthesis are upregulated

Answer 1

When the enzyme is phosphorylated then FBPase 2 is active and PFK 2 is inactive. FBPase 2 converts fructose 2,6 bisphosphate to fructose 6 phosphate. Fructose 2,6 bisphosphate is activator of major Regulatory enzyme PFK 1 of glycolysis and activation of PFK1 increases the glycolysis. since fructose 2,6 bisphosphate has been converted into fructose 6 phosphate, it is not able to activate PFK 1 that reduces the rate of glycolysis (glucose breakdown) and the synthesis of glucose by gluconeogenesis increases. Option C ( glycolysis is down regulated, gluconeogenesis is upregulated) is correct.