Biochemical characterization of the dual positional specific maize lipoxygenase and the dependence of lagging and initial burst phenomenon on pH, substrate, and detergent during pre-steady state kinetics

Immobilization of Soybean Lipoxygenase on Nanoporous Rice Husk Silica by Adsorption: Retention of Enzyme Function and Catalytic Potential

Soybean lipoxygenase was immobilized on nanoporous rice husk silica particles by adsorption, and enzymatic parameters of the immobilized protein, including the efficiency of substrate binding and catalysis, kinetic and operational stability, and the kinetics of thermal inactivation, were investigated. The maximal adsorption efficiency of soybean lipoxygenase to the silica particles was 50%. The desorption kinetics of soybean lipoxygenase from the silica particles indicate that the silica-immobilized enzyme is more stable in an anionic buffer (sodium phosphate, pH 7.2) than in a cationic buffer (Tris-HCl, pH 7.2). The specific activity of immobilized lipoxygenase was 73% of the specific activity of soluble soybean lipoxygenase at a high concentration of substrate. The catalytic efficiency (kcat/Km) and the Michaelis-Menten constant (Km) of immobilized lipoxygenase were 21% and 49% of kcat/Km and Km of soluble soybean lipoxygenase, respectively, at a low concentration of substrate. The immobilized soybean lipoxygenase was relatively stable, as the enzyme specific activity was >90% of the initial activity after four assay cycles. The thermal stability of the immobilized lipoxygenase was higher than the thermal stability of soluble lipoxygenase, demonstrating 70% and 45% of its optimal specific activity, respectively, after incubation for 30 min at 45 °C. These results demonstrate that adsorption on nanoporous rice husk silica is a simple and rapid method for protein immobilization, and that adsorption may be a useful and facile method for the immobilization of many biologically important proteins of interest.

Calcium modulates membrane association, positional specificity, and product distribution in dual positional specific maize lipoxygenase-1

This study investigates how calcium modulates the properties of dual positional specific maize lipoxygenase-1, including its interaction with substrate, association with subcellular membrane and alteration of product distribution. Bioinformatic analyses identified Asp(38), Glu(127) and Glu(201) as putative calcium binding residues and Leu(37) as a flanking hydrophobic residue also potentially involved in calcium-mediated binding of the enzyme to subcellular membranes. Asp(38) and Leu(37) were shown to be important but not essential for calcium-mediated association of maize lipoxygenase-1 to subcellular membranes in vitro. Kinetic studies demonstrate that catalytic efficiency (Vmax/Km) shows a bell-shaped dependence on log of the molar ratio of substrate to unbound calcium. Calcium also modulates product distribution of the maize lipoxygenase-1 reaction, favoring 13-positional specificity and increasing the relative amount of (E,Z)-isomeric products. The results suggest that calcium regulates the maize lipoxygenase-1 reaction by binding to substrate, and by promoting binding of substrate to enzyme and association of maize lipoxygenase-1 to subcellular membranes.

Transgenic expression of dual positional maize lipoxygenase-1 leads to the regulation of defense-related signaling molecules and activation of the antioxidative enzyme system in rice

Effects of transgenic expression of dual positional maize lipoxygenase-1 on the defense system were analyzed in rice. The activities of hydroperoxidelyase and antioxidative enzymes (superoxide dismutase, catalase, peroxidase) were increased and high levels of aldehydes including malondialdehyde were produced. The constitutive level of jasmonic was slightly increased and the constitutive salicylic acid level was decreased. Kinetic analysis of wound response indicated that the levels of jasmonic acid and salicylic acid are inversely correlated in nully transgenic rice plants, suggesting that there is an antagonistic interaction between jasmonic acid and salicylic acid. Microarray analysis indicated that several defense-related genes encoding antioxidative enzymes and pathogen-related proteins were up-regulated, and the resistance to rice blast fungus was enhanced in transgenic rice. Taken together, our results suggest that maize lipoxygenase-1 expressed in the cytoplasm plays an important role for the regulation of defense system including the antioxidative enzymes in transgenic rice, and that these effects may be mediated by reactive oxygen species generated through the enzyme-initiated catalytic peroxidation mechanism of maize lipoxygenase-1.

Cellular localization of dual positional specific maize lipoxygenase-1 in transgenic rice and calcium-mediated membrane association

The dual positional maize lipoxygenase-1 was introduced into rice and T2 transgenic plants were produced. Cellular location of maize lipoxygenase-1 in transgenic rice and effects of calcium ion on membrane association in vitro were analyzed. Localization study by confocal microscopic analysis indicated that the maize lipoxygenase-1 was localized in cytoplasm. Sucrose-density fractionation experiment and in vitro protein transport to chloroplast showed that the maize lipoxygenase-1 can be associated with chloroplast. Secondary structure alignment revealed putative calcium binding sites in the PLAT domain of maize lipoxygenase-1 and the association of the maize lipoxygenase-1 with membranes was mediated by calcium ion in vitro. Our results provide evidences for calcium-mediated translocation of dual positional LOX without chloroplast targeting sequence from cytoplasm to chloroplast in plants for the first time.