Glycogen as a fuel: metabolic interaction between glycogen and ATP catabolism in oxygen-independent muscle contraction

The main role of muscular oxygen-independent glycolysis, starting from glycogen as the initial substrate, is the production of three ATP molecules from ADP and P_i per glucosyl moiety transformed into two lactate molecules. During this catabolic process not only there is no proton release, but one proton is consumed. Metabolic acidosis occurs because the three ATP molecules are immediately hydrolysed by myosin ATPase back to 3P_i and 3ADP, to sustain contraction. As a consequence of this ATP turnover, the ATP pool (~5?mmol?kg^?1 wet weight) should remain constant. However, a bulk of experimental evidence has clearly shown that depletion of the muscular ATP pool, and accumulation of ATP catabolites occur even during short sprint bouts. In the present article the interrelationship between glycogen and ATP catabolism in anaerobic contracting muscle is discussed. It is shown how myosin ATPase plays a role not only in the mechanisms of ATP recycling through glycogen anaerobic catabolism, but also in the process of ATP depletion.