Abstract
Surface excess values for palmitoyl-coenzyme A have been determined at the air-water interface. In the bulk concentration range of 0.23 to 3.7 muM, the surface concentration of palmitoyl-CoA ranges from 0.7 to 1.4 times 10- minus 10 mol/cm-2. The molecules of palmitoyl-CoA in the surface layer behave as if they were in a monolayer with each molecule occupying a limiting molecular area of 79 A-2. The distribution of palmitoyl-CoA between bulk and surface phases can be described by a Langmuir adsorption isotherm with an equilibrium constant of 0.33 muM. This constant is identical to the apparent Km for palmitoyl-CoA in the 1-acylglycerol-3-phosphate acyltransferase reaction catalyzed by microsomes. The results of this study, together with those from earlier work, suggest that the observed saturation behavior of the enzymatic reaction reflects the formation of a positive surface excess of palmitoyl-CoA in the vicinity of the catalytic site.
Highlights
The molecules of palmitoyl-CoA in the surface layer behave as if they were in a monolayer with each molecule occupying a limiting molecular area of 79 A2
The results of this study, together with those from earlier work, suggest that the observed saturation behavior of the enzymatic reaction reflects the formation of a positive surface excess of palmitoyl-CoA in the vicinity of the catalytic site
Reactions catalyzed by membrane-bound enzymes frequently utilize substrates which are only partially soluble in water
Summary
A have been determined at the air-water interface. In the bulk concentration range of 0.23 to 3.7 PM, the surface concentration of palmitoyl-CoA ranges from 0.7 to 1.4 x lo-lo mol/cm[2]. The distribution of palmitoyl-CoA between bulk and surface phases can be described by a Langmuir adsorption isotherm with an equilibrium constant of 0.33 PM. This constant is identical to the apparent K, for pahnitoyl-CoA in the I-acylglycerol-3-. The results of this study, together with those from earlier work, suggest that the observed saturation behavior of the enzymatic reaction reflects the formation of a positive surface excess of palmitoyl-CoA in the vicinity of the catalytic site. Reactions catalyzed by membrane-bound enzymes frequently utilize substrates which are only partially soluble in water. The results obtained suggest that the velocity of the enzymatic reaction is cont,rolled by the surface concentration of substrate in the proximity of the enzyme
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