HYDROPHOBIC BINDING OF HYDROCARBONS BY PROTEINS .2. RELATIONSHIP OF PROTEIN STRUCTURE

1. 1. The binding of hydrocarbon by solutions of proteins has been found to be markedly influenced by protein structure. Determinations were made of binding of n-hepane by solutions of protein (usually 1%) in equilibrium with a layer of pure hydrocarbon. Under these conditions, bovine serum albumin bound 410 mmoles of n-heptane per 10 000 g of protein at pH 6.8 while lysozyme bound only 2 mmole per 10 000 g. β-Lactoglobulin binding was equivalent to that of bovine serum albumin, while other proteins examined had the following binding values as compared to bovine serum albumin taken as 100%: turkey ovomucoid, 42; chicken ovotransferrin, 29; serum albumin taken as 100%: turkey ovomucoid, 42; chicken ovotranchicken ovomucoid, 24; ribonuclease, 17; insulin, 9.8 (at pH 2.8); α-chymotrypsin, 8.5; bovine γ-globulin, 7.3; chymotrypsinogen-A, 7.1; ovalbumin, 2.4; and lysozyme, 0.49. 2. 2. Reduction and S-alkylation of two proteins with very low affinity, γ-globulin and lysozyme, increased the binding by a factor of 15 and 100 times respectively. Reduction and S-alkylation of two proteins with high affinity, β-lactoglobulin and bovine serum albumin, lowered the binding only slightly. Dilute acid hydrolysis of lysozyme and γ-globulin for different periods of time first increased and then decreased the binding. No changes in binding occurred with the formation of the complex between ovotransferrin and iron or the complex between α-chymotrypsin and turkey ovomucoid. 3. 3. It is concluded that peptide structure, and possibly peptide chains with hydrophobic areas available for sequestering the hydrocarbon, are necessary for hydrocarbon binding. Hydrocarbon binding appears to offer another useful analytical method for determining changes in protein structure. © 1969.