KINETIC AND THERMAL CHARACTERIZATION OF PEROXIDASE FROM PEELS OF CITRUS RETICULATA VAR. KINNOW

S. Nouren, H. N. Bhatti, I. A. Bhatti and M. Asgher

Department of Chemistry & Biochemistry, University of Agriculture, Faisalabad-Pakistan
Corresponding author email: hnbhatti2005@yahoo.com; haq_nawaz@uaf.edu.pk

ABSTRACT

In this study peroxidase was isolated from peels of Citrus reticulata var. Kinnow and partially purified using ammonium sulphate precipitation method. Kinetic and thermal characterization of the partially purified enzyme was explored. The optimum pH and temperature were found to be 6 and 55 0C respectively. The Km and Vmax values for guaiacol as substrate were found out to be 0.66 mM and 380 μmol/mL/min. Kinetics of irreversible thermal  inactivation  was studied from 60-80˚C. The enthalpy (ΔH˚) and free energy (ΔG˚) of thermal inactivation of Citrus reticulata peroxidase were 92.92 and 110.06 kJ/mol respectively at 80 ˚C. The effect of urea as inhibitor was investigated. Citrus reticulata var. Kinnow peroxidase showed retention of 84.22 % activity after 60 min with 8 M urea.  The surfactants decreased the activity of peroxidase with the exception of lemon max which enhanced the activity of enzyme. Metal ions like Mg2+, Mn2+, Cd2+, Cu2+ and Al3+ enhanced the activity of peroxidase whereas Co2+, Cr3+, Hg2+, Ca2+, Pb2+, Zn2+, Sr2+ and Ni2+ showed slightly inhibiting behaviour.
Key words: Citrus reticulate var.Kinnow peroxidase; Thermal denaturation; Enthalpy of inactivation; Free energy of inactivation; Kinetics.