Modifications induced by acylphosphatase in the functional properties of heart sarcolemma Na+,K+ pump.
Acylphosphatase purified from cardiac muscle actively hydrolyzes the phosphoenzyme intermediate of heart sarcolemma Na+,K(+)-ATPase. This effect occurred with acylphosphatase amounts (up to 800 units/mg membrane protein) that fall within the physiological range and the low value of the apparent Km (0.69 x 10(-7) M) indicates a considerable affinity of the enzyme towards this specific substrate. Acylphosphatase addition to purified sarcolemmal vesicles significantly increased the rate of Na+,K(+)-dependent ATP hydrolysis. Maximal stimulation, observed with 800 units/mg protein, resulted in an ATPase activity which was about 2-fold over basal value. The same acylphosphatase amounts significantly stimulated, in a similar and to an even greater extent, the rate of ATP driven Na+ transport into sarcolemmal vesicles. These findings lead to suppose that an accelerated hydrolysis of the phosphoenzyme may result in an enhanced activity of heart sarcolemmal Na+,K+ pump, therefore suggesting a potential role of acylphosphatase in the control of this active transport system.
Nassi
P
P
Dipartimento di Scienze Biochimiche, Università di Firenze, Italy.
Nediani
C
C
Fiorillo
C
C
Marchetti
E
E
Liguri
G
G
Ramponi
G
G
D017766:Acid Anhydride Hydrolases / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D001693:Biological Transport, Active; D002417:Cattle; D006868:Hydrolysis; D009206:Myocardium / Q000201:enzymology*; D010766:Phosphorylation; D011188:Potassium / Q000494:pharmacology; D012508:Sarcolemma / Q000201:enzymology*; D012964:Sodium / Q000378:metabolism / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D013379:Substrate Specificity; D000097024:Acylphosphatase
D017766:Acid Anhydride Hydrolases; D000255:Adenosine Triphosphate; D011188:Potassium; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D000097024:Acylphosphatase