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Regulation by Membrane Fluidity of the Allosteric Behavior of the (Ca²⁺)-Adenosine Triphosphatase from Escherichia coli

¹ Instituto de Química Biológica, Facultad de Bioquímica, Química y Farmacia, Universidad Nacional de Tucumán, Chacabuco 461, San Miguel de Tucumán, Tucumán, República Argentina, and Cátedra de Microbiología Industrial, Departamento de Tecnología Farmacéutica, Facultad de Farmacia y Bioquímica, Universidad Nacional de Buenos Aires, Junín 956, Buenos Aires, República Argentina

ABSTRACT

The allosteric properties of the membrane-bound (Ca²⁺)-adenosine triphosphatase of an unsaturated fatty acid auxotroph of Escherichia coli were studied in membranes with different fatty acid compositions. The Hill coefficient of the inhibition by Na⁺ ranged from 1.4, in the case where the auxotroph was grown with cis-vaccenic acid as supplement, to 2.8 when grown on linolenic acid. The results indicate that no fatty acid is particularly involved in the allosteric phenomena. A correlation between the values of the Hill coefficient and the double bond index or the ratio of the double bond index saturated to the fatty acids of the membrane was found. These facts are interpreted as a modulation by the membrane fluidity of the allosteric behavior of the membrane-bound enzyme. The general biological character of this phenomenon is discussed in this paper.