11.5. Pyruvate kinase
Pyruvate kinase is the third regulated enzyme of glycolysis. Pyruvate kinase is regulated by various allosteric effectors like AMP, ATP and Acetyl –CoA. A high AMP concentration (an indicator of low energy production) activates pyruvate kinase. In contrast, pyruvate kinase is inhibited by a high ATP concentration (an indicator that the cell’s energy requirements are being met). Acetyl-CoA, which accumulates when ATP is in rich supply, inhibits pyruvate kinase.
F-1,6-BP activates the Pyruvate kinase in the liver, a second example of feed forward stimulation. Alanine (a biosynthetic product of pyruvate) is an allosteric inhibitor of pyruvate kinase. Phosphorylation of pyruvate kinase is regulated by blood glucose level, just like PFK. High glucagon (low blood sugar) causes phosphorylation, which in this case renders the enzyme inactive.
11.6. Hemolytic Anemia
Pyruvate kinase deficiency causes hemolytic anemia, since red blood cells depend entirely on glycolysis for ATP synthesis. Pyruvate kinase deficiency causes accumulation of 1,3 BPG and PEP. The concentration of pyruvate and lactate are lower than normal in this disorder.
Acetyl CoA is an allosteric effector of both glycolysis and gluconeogenesis. Acetyl-CoA inhibits pyruvate kinase and reciprocally activates pyruvate carboxylase. Acetyl CoA also inactivates pyruvate dehydrogenase providing a regulatory link between glycolysis and the citric acid cycle. High concentrations of acetyl-CoA are indicative of high energy supplies. When the energy supply is high, metabolites are directed towards storage in the form of glycogen.