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Thermostability Studies of Streptomyces roseiscleroticus Glucose Isomerase

Okwuenu Prosper Chinyelum, Oparaji Emeka Henry, Onosakponome Iruoghene

This study was aimed at investigating the kinetic and thermodynamic properties of Streptomyces roseiscleroticus 
glucose isomerase and also studying the effect of a few divalent metal ion (Mg2+, Mn2+, Co2+, Cu2+, Ca2+ and Zn2+) 
concentration on the glucose isomerase activity. Glucose isomerase was produced from Streptomyces roseiscleroticus 
using a submerged fermentation system. The crude glucose isomerase was purified 6.55 fold with specific activity of 
696 U/mg protein and percentage yield of 2.17 after ammonium sulphate precipitation (80% saturation), dialysis, 
ion-exchange chromatography (DEAE-Cellulose) and gel filtration (Sephadex-G100). The purified glucose isomerase 
had optimum pH and temperature of 7.5 and 60°C, respectively. A simple first order reaction which assumes a 
biphasic thermo inactivation curve was used to study the kinetic and thermodynamic properties of the enzyme. 
Activation energy of denaturation (Ea), 19.845 KJ/mol was obtained, with a Z-value of 0.0073. Thermodynamic 
parameters showed that, the enthalpy of activation of denaturation (∆H) was 17.243, 17.160, 17.077, 16.993 and 
16.911 KJ/mol at 303°K, 323°K, 333°K, 343°K and 353°K, respectively. The Gibbs free energy values were greater 
than zero (∆G>0) at all the temperatures under study, while the entropy of inactivation were less than zero (ΔS<0) at 
all the temperatures under study. Studies on the effect of divalent metal ions on glucose isomerase activity showed 
that, Mg2+, Mn2+, Co2+ and Cu2+ enhanced glucose isomerase activity at increasing concentration, while Ca2+ and 
Zn2+ decreased glucose isomerase activity with Ca2+ showing the greatest inhibition at all concentrations. These 
findings indicate that Streptomyces roseiscleroticus glucose isomerase is a stable enzyme and could be useful for 
industrial purposes and applications, especially for sugar syrup production and bioethanol fermentation