Biochimica et Biophysica ,4cta, 415 (1975) 231-251 © Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands BBA 85148 REGULATION OF ALLOSTERIC MEMBRANE-BOUND ENZYMES THROUGH CHANGES IN MEMBRANE LIPID COMPOSITION RICARDO N. FARIAS"*, BERNABI~ BLOJ"**, ROBERTO D. MORERO', FAUSTINO SI~IERIZ"*** AND RAI3L E. TRUCCO b't "Instituto de Qubnica Biol6g."ca, Facultad de Bioqulmica, Quimica y Farmacia, Universidad Nacional de Tucum6n, Chacabuco 461, San Miguel de Tucumdn and bLaboratorio de Microbiologia Industrial, Departamento de Tecnologia Farmaceutica, Facultad de Farmacia 3, Bioquimica, Universidad Nacional de Buenos Aires Junin 956, Buenos Aires (Argentina) (Received January 3rd, 1975) CONTENTS I. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232 ii. Effect of fat-free diet on cooperativity of membrane-bound enzymes . . . . . . . . . . 233 111. Relationship between membrane lipid fluidity and enzyme cooperativity . . . . . . . . 234 A. Mammalian membranes . . . . . . . . . . . . . . . . . . . . . . . . . . . 235 1. Changes in fatty acid composition . . . . . . . . . . . . . . . . . . . . . 235 2. Changes in cholesterol content . . . . . . . . . . . . . . . . . . . . . . . 236 B. Bacterial membranes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237 IV. Some properties of the cooperative enzymes that showed correlation with the membrane lipid fluidity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238 A. Localization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238 B. Dependence on the lipids for enzymatic activity . . . . . . . . . . . . . . . . . 239 V. Influence of membrane integrity for lipid effect on the enzyme cooperativity "Macro- effector" . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240 VI. The application of Hill coefficient measurement as a probe for membrane structure... 243 A. Arrhenius plots and Hill plots of the membrane-bound enzymes . . . . . . . . . . 244 B. Change of membrane fluidity and Hill coefficient in response to hormone action . . 245 VII. Speculations on the membrane allosteric control . . . . . . . . . . . . . . . . . . 246 A. Possible general nature of membrane allosteric control phenomena . . . . . . . . . 246 B. Specilic functions of the enzymes studied . . . . . . . . . . . . . . . . . . . 247 1. Acetylcholinesterase . . . . . . . . . . . . . . . . . . . . . . . . . . . 247 2. ATPases associated to vectorial ion-transport systems . . . . . . . . . . . . . 247 3. ATPases associated to vectorial electron-transport systems . . . . . . . . . . . 248 ACKNOWLEDGEMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249 * Career Investigator of the Consejo Nacional de lnvestigaciones Cientificas y T6cnicas. ** Present address: Division of Nutritional Science, Cornell University, Savage Hall, Ithaca, New York. *** Present address: Microbiology Department, Queen Elizabeth College, University of London. t Present address: lnstituto Naeional de Tecnologia Industrial, Libertad 1235, Buenos Aires