Kinetics of the interactions of AMP deaminase with fatty acids.

The effect of fatty acids with various structure and length in the hydrocarbon chain on the purified AMP deaminase from bovine brain was investigated. All the saturated fatty acids and unsaturated ones of trans configuration, longer than 16 in the hydrocarbon chain, were activators of the enzyme, while the unsaturated fatty acids of cis configuration including oleic, linoleic, linolenic, arachidonic, and palmitoleic acids acted as inhibitors. The methyl esters of fatty acids showed no effect on the enzyme, suggesting that a free carboxyl group of fatty acid is required for the effect of fatty acid on the enzyme. The activation and inhibition of AMP deaminase by fatty acids are qualitatively and quantitatively accounted for by a “partial noncompetitive” mechanism with respect to the substrate AMP; best fit theoretical curves were obtained for the activation and inhibition of the enzyme by fatty acids. A close correlation was observed between the fatty acid conformation (or the parameter defined by the distance from carboxyl carbon to w carbon atom) and the reaction rate constant for the enzyme l substrate l fatty acid (ESI) complex. It is suggested that the nonpolar interactions of each fatty acid with the same hydrophobic region induce the conformational change of the enzyme, which results in the increase or decrease in the breakdown rate of the ES1 complex.