Inhibitory effect of superoxide radicals on cardiac myofibrillar ATPase activity.
The superoxide radicals generated by the xanthine oxidase reaction reduced the myofibrillar Ca2+-ATPase activity. This negative effect was prevented by superoxide dismutase or by dithiothreitol, a protective thiol compound. Partial protection was achieved by catalase, while mannitol was ineffective. The myofibrillar Ca2+-ATPase exposed to O2-. radicals did not modify the affinity for Ca2+ while it showed a remarkable reduction of Vmax measured at the saturating level of Ca2+. The O2-. inhibited myofibrillar ATPase showed a higher value of Km for the cofactor associated to a reduced value of Vmax when studied in the presence of increasing concentration of ATP. Thus, circumstances that enhance the production of cardiac O2- radicals can be considered a negative metabolic event capable of depressing the myofibrillar Ca2+-ATPase activity.
D000205:Actomyosin / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000037:antagonists & inhibitors*; D000818:Animals; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D006352:Heart Ventricles / Q000378:metabolism; D007700:Kinetics; D009206:Myocardium / Q000201:enzymology*; D009210:Myofibrils / Q000201:enzymology*; D011817:Rabbits; D013481:Superoxides / Q000494:pharmacology*
D013481:Superoxides; D000205:Actomyosin; D000251:Adenosine Triphosphatases; D000252:Calcium-Transporting ATPases