Allosteric Changes of p-Nitrophenylphosphatase from Rat Erythrocytes in Fat Deficiency

Abstract

Abstract The kinetic properties of the p-nitrophenylphosphatase of red cell ghosts from rats fed fat-sufficient and fat-deficient diets were investigated. With this system the enzyme shows hyperbolic saturation curves. In the fat-sufficient case, positive cooperativity with n g 1.5 for K+ and negative cooperativity with n l -1.5 for F- were observed. Evidence for a different allosteric transition in the p-nitro-phenylphosphatase from fat-deficient rats is supported by the following facts: (a) values of n g -1.5 in F- inhibition and (b) nonsigmoidal kinetics for K+ activation with n l 1.5. In the activation by K+, the heterotropic effect of F- and of the substrate alters the values of n and K0.5 in fat-deficient rats but in fat-sufficient rats the corresponding effect is only on the K0.5 values. Arrhenius plots for the p-nitrophenylphosphatase between 7 and 45° showed for the enzyme from fat-sufficient rats an inflection point at 30°; for the p-nitrophenylphosphatase from deficient animals two inflection points were observed, one at 30° and another at 37°. Evidence is presented showing that in fat-deficient rats the p-nitrophenylphosphatase of the red cell ghost has an allosteric transition different from the corresponding controls.