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SJOERD L. BONTING; Na-K Activated Adenosinetriphosphatase and Active Cation Transport in the Lens. Invest. Ophthalmol. Vis. Sci. 1965;4(4):723-738.
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The enzyme Na-K activated ATPase, which is closely related to the active transport system of sodium and potassium in erythrocytes, nerve and other tissues, occurs in relatively high activities in the epithelium of cat, calf, and rabbit lens. No significant activity could be detected in anterior and posterior capsule, cortex, and nucleus. Various properties of the enzyme system were determined and compared with corresponding properties of the transport system reported by other investigators. Both enzyme and transport system are located in the lens epithelium. They are both inhibited by ouabain, and there is good agreement between the half-maximal inhibition concentrations for the two systems in calf as well as in rabbit lens. In both enzyme and transport system Rb can replace K. In rabbit lens the pH optimum of the enzyme is 7.3 as compared to 7.5 for Rb uptake. The temperature coefficients of the two systems are 2.4 and 2, respectively. Ratios of equivalents cation transported to moles ATP hydrolyzed by the epithelial Na-K ATPase ranged from 2.51 to 4.15 (average 3.07) for the three cations transported in calf and rabbit lens. It is concluded that the epithelial Na-K ATPase and the active cation transport system of the lens are identical or very closely related. The relation with energy metabolism, the mechanism of action, the intracellular location, and the function of the Na-K ATPase system were discussed.
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