Hydrophobic binding of hydrocarbons by proteins. I. Relationship of hydrocarbon structure

Abstract

1. 1. The interactions between proteins and a variety of hydrocarbons were studied. An improved procedure was developed to determine the amount of hydrophobic substance absorbed or dissolved in the protein solution. This procedure involves the direct injection of the hydrocarbon-protein mixtures into a gas-liquid chromatographic apparatus. 2. 2. Binding studies were done with bovine serum albumin and β-lactoglobulin. With homologous alkanes, the amounts bound decreased as chain length was increased from C 7 to C 13, especially with β-lactoglobulin. Larger amounts of branched-chain alkanes were bound by bovine serum albumin than by β-lactoglobulin. Both alicyclic and aromatic hydrocarbons were more soluble in bovine serum albumin than in β-lactoglobulin. No preferential binding was observed for cis- versus trans-isomers of dimethylcyclohexane. Similarly, there were no marked differences in binding of o-, m-, or p- xylene . 3. 3. The procedure was used to study the effect of hydrocarbon concentration on binding by β-lactoglobulin. The reciprocal plot of the binding isotherm of n- heptane was linear and the Scatchard plot gave a value of 1.35 for the number of strong binding sites per mole of β-lactoglobulin. Plots with benzene, however, indicated that binding approached infinity at high benzene concentrations. The results demonstrate that interactions between a wide variety of hydrocarbons and proteins can be studied by the general techniques described.