A study on the lipid-coating of lipases

A quantitative study on the lipid-coating of lipases together with soluble globular proteins such as bovin serum albumin and γ-globulin was carried out using a synthetic lipid, dioleyl glucosyl L-glutamate, by means of a solution depletion method. Complexation isotherms similar to Langmuir-type adsorption isotherms with saturation plateaus were derived from the results, and additional parameters, such as the number of complexation sites (n) and the complexation constant (K), were also evaluated. Together, these data provide a more detailed description of the lipid-coating process. For example, it is possible to predict the coverage of proteins, the number of lipid molecules bound per protein molecule, the maximum values of this number, and the compositions of the precipitated lipid-coated protein under the given lipid-coating conditions. The positive correlation among protein surface hydrophobicity, coverage of protein, and diminished amounts of the lipid molecules required to hydrophobize an original protein confirms that the affinity between protein and lipid in this process is primarily hydrophobic, and that the lipid-coating of enzymes seems to be limited by intrinsic structural features of the enzymes themselves. The reactivity of the lipid-coated lipase in organic solvents depends on the pH of the aqueous solution in the complexation and shows the same profile as that of native lipase in aqueous solution, while the coverage of lipases is scarcely influenced by aqueous pH. The coverage of lipase had no influence on specific activity or enantioselectivity in the enzymatic reaction in organic solvent.