Ficus sycomorus latex: A thermostable peroxidase

Abstract

Peroxidase from sycamore fig Ficus sycomorus latex (POLI) was purified by heat treatment, anion exchange chromatography and molecular exclusion chromatography. The purity was determined from high specific activity (9166 units/mg protein), purification fold (28), RZ value 3.1 and a single band in native polyacrylamide gel electrophoresis (PAGE), sodium dodecyl sulfate (SDS)-PAGE and visualized peroxidase activity on the PAGE. POLI had molecular mass of 43 kDa. Substrates commonly used in immunodiagnostic kits as 2,2-azino-bis [3-ethyl- benzothiazoline-(6)-sulfonic acid] (ABTS), 4-chloro-1- naphthol (4C-1N), o-phenylenediamine (OPD) and 3,3`,5,5`- tetramethylbenzidine (TMB) were found to be the best substrates for the enzyme. The K_m for catalysis of H₂O₂ was 1.2 mM. The catalytic efficiency (Vmax/Km) for POLI was found to follow the order: ABTS, 4C-1N, OPD, TMB, guaiacol, paminoantipyrine, o-dianisidine and pyrogallol. The enzyme showed a broad pH optimum ranged from pH 5.5 to 7.0. The optimal temperature for the enzyme was 35 to 40°C. POLI showed highest thermal stability. No loss of enzyme activity was recorded up to 60°C, whereas only 20% of enzyme activity was lost at 70 to 90°C. The thermal inactivation profiles of POLI demonstrated that the enzyme had higher thermal resistance. The peroxidase activity was slightly enhanced by low concentration of Ca²⁺, Ni⁺² and Mg²⁺ and high concentration of Mn²⁺. Fe⁺³, Zn⁺², Hg⁺² caused slightly inhibitory effects. In conclusion, sycamore fig latex will be a new and potential source for a peroxidase enzyme.

Key words: Ficus sycomorus, latex, peroxidase, purification, characterization.