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Heterogeneous Effect of Dietary Cholesterol on Acetylcholinesterase and ATPases of Rat Erythrocytes: Arrhenius Plots^1,2,

Instituto de Química Biológica, Facultad de Bioquímica, Química y Farmacia, Universidad Nacional de Tucumán, Chacabuco 461, San Miguel de Tucumán, Tucumán, Argentina

The influence of cholesterol on the Arrhenius plot of acetylcholinesterase was studied in erythrocytes from five groups of male rats fed different fat-supplemented diets. When the rats were fed a purified diet supplemented with 5% corn oil (group A) or lard (group B) or a commercial stock diet (group C), the Arrhenius plot of the enzyme exhibited a single break around 20° with a lower slope at higher temperatures. When the diets were supplemented with 1% cholesterol, the enzyme from group A exhibited two breaks, at 23° and 27°, but remained unchanged in diets B and C. The enzyme from rats fed essential fatty acid deficient diets (either a purified fat-free diet or one supplemented with 5% hydrogenated beef fat) from weaning exhibited a break point around 28°, which shifted to around 18° when the diets were supplemented with 1% cholesterol. The slopes were also different after cholesterol feeding. The Arrhenius plot of the Mg ATPase from corn oil fed rats was linear between 4° and 40° but the enzyme from lard-fed rats showed a break point around 30°. When the rats were fed the same diets plus 1% cholesterol the Arrhenius profiles became identical, exhibiting two break points at 27° and 35°. Similar changes were detected for the (Ca + Mg)ATPase. The changes found by cholesterol feeding could be reproduced by loading the membranes of control rats with cholesterol in vitro. The heterogeneous response of cholesterol to different enzymes in rats fed the same diet and to the same enzyme from rats fed different diets is related to the heterogeneous distribution of lipids in the membrane and the asymmetric localization of the enzymes in the membrane.

KEY WORDS: • cholesterol • diet • acetylcholinesterase • ATPases

¹ Supported by Grants from the Consejo Nacional de Investigaciones Científicas y Técnicas and Secretaría de Ciencia y Técnica de la Universidad Nacional de Tucumán (Argentina).

² A partial account of this work has been given at the International Symposium on Function and Biosynthesis of Lipids, 1976 Sierra de la Ventana, Argentina. The Proceedings have been published: Function and Biosynthesis of Lipids. N. G. Bazán, R. R. Brenner, and N. M. Giusto, Editors. Plenum Press, New York and London 1977.

³ Career Investigator of the Consejo Nacional de Investigaciones Científicas y Técnicas.

Manuscript received 11 January 1978.