Question

Calcium ions participate in fine control of respiration in aerobic mammalian muscle. What is/are the metabolic control mechanisms by which an increased Ca2+ concentration rapidly enhances the rate of pyruvate oxidation to 3CO2 molecules in contracting mammalian muscle cells (myocytes)?

Answer 1

Increased Ca2+ concentration enhances pyruvate oxidation in mammalian muscle cells through the activation of the pyruvate dehydrogenase complex and stimulation of the citric acid cycle.

Step-by-step explanation:

Calcium ions play a crucial role in the regulation of metabolic processes in aerobic mammalian muscle cells. Increased Ca2+ concentration rapidly enhances the rate of pyruvate oxidation to 3CO2 molecules in contracting myocytes through two main metabolic control mechanisms:

1. Activation of the pyruvate dehydrogenase complex (PDC): Elevated Ca2+ levels stimulate the phosphorylation of PDC, leading to its activation. This results in increased conversion of pyruvate to acetyl-CoA, which further enters the citric acid cycle for complete oxidation to CO2.
2. Stimulation of the citric acid cycle: Ca2+ ions enhance the activity of isocitrate dehydrogenase, a key enzyme in the citric acid cycle. This promotes the conversion of isocitrate to alpha-ketoglutarate, facilitating the generation of NADH and FADH2 molecules that participate in oxidative phosphorylation and ATP production.