5′‐Nucleotidase is activated upon cholesterol‐depletion of liver plasma membranes

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Abstract
The cholesterol content of rat liver plasma membranes was manipulated using either cholesterol-free or cholesterol-enriched liposomes. Removal of cholesterol from the membranes led to a marked increase in 5′-nucleotidase activity. However, increase in cholesterol content failed to exert any significant effect on 5′-nucleotidase activity. Arrhenius plots of the activity of the native enzyme exhibited a break at around 28°C with the activation energy of the reaction less above this temperature than below. In cholesterol-depleted membranes a single break at around 26°C was observed with activation energies greater above this temperature than below it. In cholesterol-enriched membranes Arrhenius plots were linear over the range examined. It is suggested that the lipid environment of the external half of the bilayer only influences 5′-nucleotidase activity in these membranes and that cholesterol exerts controlling effects on both the activity and conformation of the enzyme in native membranes.