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Fourier Transform Infrared Study of Lipoxygenase Conformation in Organic Solvent Media

Volume 60, Number 2 (Feb. 2006) Page 168-173

Vega, Mireille; Ismail, Ashraf; Sedman, Jacqueline; Kermasha, Selim


The secondary structure of commercially purified soybean lipoxygenase (EC 1.13.11.12) was investigated in selected monophasic organic solvents, including chloroform, methanol, acetonitrile, hexane, and octane. The Fourier transform infrared (FT-IR) spectra of the enzyme obtained in chloroform, methanol, and acetonitrile showed an absorption band at 1617 cm−1 indicative of significant protein aggregation, whereas spectra of lipoxygenase in hexane and octane exhibited substantially less aggregate formation. Variable-temperature infrared studies of lipoxygenase in D2O show that the predominately α-helical structure of the protein undergoes an irreversible transition to intermolecular β-sheet at and above 65 °C. Chemical imaging technology employing an FT-IR spectrometer equipped with an infrared microscope and a focal-plane array detector was used to examine the changes in the secondary structure of lipoxygenase at the water-hexane interface in the presence and absence of substrate. The secondary structure of lipoxygenase at the hexane-water interface was comparable to that of the structure of lipoxygenase in D2O after exposure of lipoxygenase solution to hexane.