Lipase made active in hydrophobic media

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Abstract
Enzymes are distinguished from other catalysts by their high substrate specificity. This is a great asset when one wants to apply them for syntheses of various compounds. Their usage, however, generally is limited to hydrophilic reaction media, because they usually are not soluble and active in hydrophobic media. Recently, we have been able to make various enzymes soluble and active in highly hydrophobic organic solvents. The key to this success is the chemical modification of enzymes with an amphipathic synthetic polymer, polyethylene glycol. The activated polymers can be attached to enzymes in aqueous buffer solutions, and once enzymes are modified they become soluble and active in various organic solvents such as benzene, toluene and cholorinated hydrocarbons and exhibit high enzymic activities in these organic solvents. Modified hydrolytic enzymes catalyzed the reverse reaction of hydrolysis in organic solvents. The modified lipase catalyzed various ester synthesis reactions. Because the reactions were conducted in the pure solvent system, it also was possible to study the kinetics and the substrate specificity for ester synthesis reaction. It also catalyzed the polymerization of a hydroxy group containing carboxylic acid due to the bifunctional nature. The modified lipase catalyzed ester exchange between an ester and an alcohol, between an ester and a carboxylic acid and between two esters in organic solvents. When the two substrates for ester exchange were liquid, the reaction could take place without organic solvents. The modified lipase catalyzed an ester exchange reaction between trilaurin and triolein when dissolved in these substrates. Dilauroyl‐monooleoylglycerol and monolauroyl‐dioleoyl‐glycerol were formed from these two substrates in the presence of the modified lipase. The modified enzyme was extremely thermostable in its substrates. In the ester synthesis and ester exchange reactions, a trace amount of water was necessary for expression of the enzymic activity. It is suggested that the amphipathic polymer molecules retained water in close proximity to the enzyme.

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