ABSTRACT
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 D(2)O show that the predominately alpha-helical structure of the protein undergoes an irreversible transition to intermolecular beta-sheet at and above 65 degrees 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 D(2)O after exposure of lipoxygenase solution to hexane.
Subject(s)
Lipoxygenase/analysis , Lipoxygenase/chemistry , Organic Chemicals/chemistry , Solvents/chemistry , Spectroscopy, Fourier Transform Infrared/methods , Colloids/analysis , Colloids/chemistry , Protein Conformation , Protein Structure, SecondaryABSTRACT
The immobilization and biocatalysis of commercially purified soybean lipoxygenase (LOX) type I-B (EC 1.13.11.12) were investigated in organic solvent media. The results showed that the highest immobilization efficiencies of LOX, 30.6 and 29.3%, were obtained with DEAE-cellulose and modified Eupergit C250L supports, respectively. The biocatalysis of free and immobilized (Eupergit C250L/EDA) LOXs was investigated in different mixtures of hexane and a selected cosolvent (95:5 [v/v]). The results showed a 1.5 and a 1.6 increase in the activity of free and immobilized LOXs, respectively, using a mixture of hexane and 1,4-dioxane compared with that in hexane alone; however, cosolvents, including 2-octanone, 2-heptanone, 2-butanone, and cyclohexanone, displayed an inhibitory effect on LOX activity. In the mixture of 1,4-dioxane and hexane, LOX activity was dependent on the cosolvent concentration, which was increased with 1,4-dioxane up to 5% (v/v). The threshold 1,4-dioxane concentration (C50) and the incubation period (T50) at which 50% of the maximal enzyme activity was obtained for the free and immobilized LOXs were 6.7 and 8.9% (v/v) and 9.1 and 17.0 min, respectively.
