Effect of lipid on the access of ATP and calcium to the delipidated Ca++-ATPase of intestinal brush border membrane. |
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Authors: | M Kurebe |
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Institution: | Department of Pharmacology, School of Pharmaceutical Sciences, Kitasato University, Minato-ku, Tokyo 108, Japan |
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Abstract: | The delipidated Ca++-ATPase prepared from intestinal brush border membranes showed a higher activity of Ca++-independent ATPase, a lower Km value for ATP and a higher Km value for Ca++ than its original membrane Ca++-ATPase. The addition of phosphatidylcholine re-activated the delipidated Ca++-ATPase to approximately 89 % of its original membrane Ca++-ATPase activity but did not restore the affinity for Ca++. This phospholipid raised the Km value for ATP but had little effect on the Km value for Ca++. Palmitic acid elevated the Km value for Ca++ but did not change the Km value for ATP. Kinetic analyses of these data suggest that the hydrocarbon chain of phosphatidylcholine is an important rate-limiting factor for the access of Ca++ to the enzyme and the polar head groups of phosphorylcholine and ester bond may be the factor for the access of ATP. |
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