Spectroscopic investigation of lipase from Pseudomonas cepacia solubilizedin 1,4-dioxane by non-covalent complexation with methoxypoly(ethylene glycol)

Lipase from Pseudomonas cepacia was made soluble in 1,4-diaxane by lyophili zation of the enzyme from aqueous solutions containing methoxypoly(ethylene glycol) (PEG). The solubility of the enzyme-PEG complex depended both on p rotein concentration and PEG protein ratio. Intrinsic protein fluorescence and far- and near-UV circular dichroism revealed that not only did the enzy me not unfold in the organic solvent, but rather became more compact. This was seen by the slight quenching of fluorescence intensity and by the enhan cement of the near-UV circular dichroism negative signals, which are indica tive of stronger interactions of tryptophanyl and/or tyrosyl residues among themselves or with other parts of the enzyme molecule. The specific activi ty of the lipase-PEG complex in the organic solvent was at least 2 orders o f magnitude higher than that of the enzyme powder. This can be attributed b oth to the maintenance of native conformation and to enzyme dissolution in the reaction medium which should minimize possible limitations to enzyme-su bstrate interactions. (C) 1999 John Wiley & Sons, Inc.