Modification of lipase from Candida cylindracea with dextran using the borane-pyridine complex to improve organic solvent stability

In this study, a commercial lipase derived from Candida cylindracea was chemically modified with dextran by conjugating epsilon-amine in the lysine residue with the carbonyl residue in oxidized dextran using the borane-pyridine complex as a reducing agent to increase the hydrophilicity of the microenvironment around the lipase in the presence of organic solvents. The degree of modification (53.2%), amount of dextran (0.66 g/g-lipase), specific activity (similar to that of the unmodified lipase), and stability in the presence of ethanol and 2-propanol (the half-lives were 2.24 and 1.86 times longer than those of the unmodified lipase) were higher for the lipase modified at pH 8.0 than for the lipases modified at other pH levels. Following modification with dextran at pH 8.0, the stability of the modified lipase was higher than that of the unmodified lipase in the presence of 25% (v/v) DMSO, ethanol, 2-propanol, toluene, n-hexane, and isooctane (the half-lives were 1.45, 2.24, 1.86, 1.76, 2.67 and 2.95 times longer than those of the unmodified lipase). Therefore, chemical modification with polysaccharides such as dextran using the borane-pyridine complex as a reducing agent could be a promising approach for improving the organic solvent stability of enzymes.