The effect of temperature on the activity of the adenylate cyclase system of liver plasma membranes |
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Authors: | J A Pliego B Rubalcava |
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Institution: | Biochemistry Department, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, P.O. Box 14-740, México 14, D.F. Mexico |
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Abstract: | The rat liver adenylate cyclase system shows a discontinuity in the Arrhenius plots at 20°C in the nonstimulated activity (basal) with activation energies of 16 and 28 Kcal/mole. The discontinuity disappears when the enzyme is stimulated either by glucagon, sodium fluoride, 5′ guanylyl-imidodiphosphate or glucagon plus 5′ guanylyl-imidodiphosphate and the energy of activation was the same with all the compounds tested. If the activator was initially in contact with the membranes at 0°C the energy of activation was similar to that observed below the break (26 Kcal/mole) but it changed to that above the break if the compound contacted the membranes at temperatures above the break (22–24°C). We discuss the possibility of two different conformations of the enzyme; both conformations can be “frozen” by any of the compounds tested, “isolating” the enzyme from any subsequent physical change of the membrane due to temperature. |
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Keywords: | To whom correspondence should be addressed |
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