Effect of metal ions on the activity of cellulase produced by Aspergillus niger using Arachis hypogaea shells

Abstract

Cellulases have attracted much interest because of the diversity of their applications but the major constraint against the use of cellulase is the high cost of production. There is need for certain parameter to be optimized as well as some cofactors that will enhance cellulase production. Therefore, this study investigated the effect of metal ions on the activity of cellulase produced by Aspergillus niger using Arachis hypogaea shells with a view to increase cellulase production. The kinetic properties (K_m and V_max) of cellulase in the presence of some cations (Na⁺, K⁺, Mg²⁺, Cu²⁺, Zn²⁺, Ca²⁺, Fe²⁺, Mn²⁺, Co²⁺) and anions (CO₃^2-, Cl^-, and SO₄^2-) were investigated. The presence of anions (CO₃^2-, Cl^- and SO₄^2-) decreased the activity of cellulase. Cations like Na⁺ activated cellulase activity at a concentration above 1 mM while K⁺ did not affect the cellulase activity. Divalent cations such as Mg²⁺, Zn²⁺, Cu²⁺, Ca²⁺ and Fe²⁺ inhibited the activity of enzyme. Mn²⁺ and Co²⁺ enhanced the activity of purified cellulase at all the concentrations investigated. Fitting of the data to Michaelis-Menten kinetics showed that Mg²⁺ competitively inhibited cellulase (K_m = 0.12 mg/ml and V_max = 1.66 U/ml) while Zn²⁺, Cu²⁺, Ca²⁺ and Fe²⁺ noncompetitively inhibited cellulase. Cellulase was also inhibited by mercaptoethanol and some surfactants such as DMSO, Triton X and Tween 20. The present study has shown that divalent cations such as Mg²⁺, Zn²⁺ and Cu²⁺, Ca²⁺ and Fe²⁺ inhibited the activity of enzyme while Mn²⁺ and Co²⁺ enhanced the activity of purified cellulase at all the concentrations investigated.