Kinetic and thermodynamic properties of membrane bound Ca-ATPase with low affinity to calcium in cardiac sarcolemma; response to global ischemia of the heart.
Thermodynamic and kinetic properties of membrane bound Ca-ATPase with low affinity to calcium in cardiac sarcolemma were investigated with respect to the effect of global ischemia on the heart. Energy barrier for ATP hydrolysis catalyzed by the Ca-ATPase was slightly higher in hearts subjected to ischemia, as it was evident from increased values of activation energy. Ischemia also induced a time dependent decrease in the activity and maximum velocity (Vmax) value of Ca-ATPase. The depression of enzyme activity was evident as early as 15 minutes after the onset of ischemia. After 30 minutes of ischemia the decrease in Vmax slowed down, probably due to an "adaptational" decrease of the Km value for Ca-ATPase. This phenomenon may be interpreted as a mechanism by which the enzyme attempts to keep working in a situation when the supply of ATP is insufficient.
Vrbjar
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N
Department of Biochemistry, Slovak Academy of Sciences, Bratislava.
Dzurba
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A
Ziegelhöffer
A
A
D000818:Animals; D002118:Calcium / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002462:Cell Membrane / Q000201:enzymology; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D017202:Myocardial Ischemia / Q000201:enzymology*; D009206:Myocardium / Q000201:enzymology*; D051381:Rats; D012044:Regression Analysis; D012508:Sarcolemma / Q000201:enzymology*; D013816:Thermodynamics
D000252:Calcium-Transporting ATPases; D002118:Calcium