Kinetic Modifications of the Acetylcholinesterase and (Ca2+ + Mg2+)-ATPase in Rat Erythrocytes by Cholesterol Feeding

The influence of cholesterol on the membrane-bound acetylcholinesterase and (Ca2+ + Mg2+)-ATPase was studied in erythrocytes of five groups of male rats fed different fat-supplemented diets. Two groups of rats were fed essential fatty acid (EFA) sufficient diets with 5% lard or corn oil as the dietary fat, and two groups were fed EFA-deficient diets: a basic, fat-free diet and the same diet supplemented with 5% hydrogenated beef fat. One additional group of rats was fed a stock diet. The kinetic changes recorded were in the degree of the cooperativity of the inhibition by F- of the acetylcholinesterase and the activation by Ca2+, and by Mg2+ of the (Ca2+ + Mg2+)-ATPase. The kinetic behavior of the enzymes was only modified by cholesterol feeding when they were bound to a membrane with a high fatty acid fluidity (e.g. derived from rats fed the corn oil-supplemented diet). The enzymes from a membrane with a low fatty acid fluidity (e.g. derived from rats fed a lard-supplemented diet) were not altered by cholesterol feeding. The changes were noticeable after 24 hours of cholesterol feeding. It is suggested that the in vivo cholesterol sites are involved in a regulatory mechanism for mammalian membrane-bound enzymes.