Endurance-training induced changes in skeletal muscle phosphoglycerate kinase of old Wistar rats

Sufficiently intense, long-term, endurance training has been shown in several studies to induce a variety of adaptations in skeletal muscle, including a substantial restoration of the activities of several muscle enzymes which are known to be modified during biological aging. This activity-restoration may reflect either an increase in the amounts of enzyme proteins or an enhancement of the specific activities of these molecules. The present study examined the effect of long-term endurance training on the status of phosphoglycerate kinase in skeletal muscle of old rats, as compared with the enzyme isolated either from non-trained old or young animals. The kinetics of heat inactivation, which differ markedly between young and old forms of phosphoglycerate kinase, were used as a sensitive probe for the status of the enzyme. The results reveal a remarkable similarity between the heat inactivation patterns of phosphoglycerate kinase from the muscle of old, exercise-trained rats and enzyme purified from young animals, while enzyme samples isolated from sedentary old animals are significantly more heat-stable. Adaptation to endurance-training is thus evident at the molecular level, and maintains phosphoglycerate kinase in its young form. The aging of this enzyme has been previously shown to involve only conformational changes, which develop following a reversible partial oxidation of reactive cysteine residues. Whether the adaptation of the enzyme to endurance-training results from enhancement in its turnover rate (i.e., dwell time in the cell becoming too short for modifications to develop) or is due to increased protection against oxidation (being the first step in the enzyme's aging) remains to be studied.