Fourier-transform infrared spectroscopy study of dehydrated lipases from Candida antarctica B and Pseudomonas cepacia

Fourier-transform infrared (FT-IR) spectroscopy was employed to investigate potential lyophilization-induced changes in the secondary structure of lip ases from Candida antarctica B and Pseudomonas cepacia. The secondary struc ture elements were determined by curve fitting of the amide III bands of th e two lipases in the lyophilized state in KBr pellets and in solution. It w as found that lyophilization decreased the alpha-helix and increased the be ta-sheet content. However, FT-IR analysis of crosslinked enzyme crystals of Pseudomonas cepacia lipase also indicated an increase in the beta-sheet co ntent, which appears despite the fact that the enzyme, being in the crystal lized state, should possess native conformation. This result partially ques tions the suitability of FT-IR for analysis of the structure of solid prote ins, at least as far as the beta-sheet content is concerned, because it is possible that the method overestimates the beta-sheets by measuring other h ydrogen-bonded nonperiodic intermolecular structures. No significant modifi cation was observed when lipase from Pseudomonas cepacia was lyophilized in the presence of methoxypoly(ethylene glycol). (C) 1999 John Wiley & Sons, Inc.