Differences in Michaelis-Menten kinetics for different cultivars of maize during cyanide removal

Abstract

Knowledge of the kinetic parameters, the half-saturation constant (Km) and the maximum metabolic capacity (vmax), is very useful for the characterization of enzymes and biochemical processes. Little is known about rates of which vegetation metabolizes environmental chemicals. It is known, however, that vascular plants possess an enzyme system that detoxifies cyanide by converting it into the amino acid asparagine. This study investigated the differences in Michaelis-Menten kinetics of cyanide removal by different cultivars of maize. Detached leaves (1.0 g fresh weight) of seven different cultivars of maize (Zea mays L.) were kept in glass vessels with 100 mL of aqueous solution spiked with potassium cyanide at 25±0.5 °C for 28 h. Four treatment concentrations of cyanide were used, ranging from 0.43 to 7.67 mg CN L-1. The disappearance of cyanide from the aqueous solution was analyzed spectrophotometrically. Realistic values of Km and vmax were estimated by a computer program using non-linear regression treatment. Lineweaver-Burk plots were also used to estimate the kinetic parameters for comparison. Using non-linear regression treatments, values of vmax and Km were found to be between 10.80 and 22.80 mg CN kg-1 h-1, and 2.57 and 7.09 mg CN L-1, respectively. The highest vmax was achieved by the cultivars HengFen 1, followed by NongDa 108. The lowest vmax was demonstrated by JingKe 8. The highest Km was found in NongDa 108, followed by HengFen 1. The lowest Km was associated with JingKe 8. Results from this study indicated that significant removal of cyanide from an aqueous solution was observed in the presence of plant materials without apparent phytotoxicity, even at the high concentration of cyanide used in this study. All maize cultivars used in this study were able to metabolize cyanide efficiently, although with different metabolic capacities. Results also showed a small variation of metabolic rates between the different cultivars. This leads to the conclusion that plants can be used as a phytoremediation agent in the detoxification of cyanide, presenting a feasible option for cleaning up soils and water contaminated with cyanide. © 2006 Elsevier Inc. All rights reserved.