الفهرس 
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Abstract
Abstract
A cationic peroxidase from Euphorbia tirucalli latex
(ELP) has been purified to homogeneity using chromatography
on Sephacryl S-200 and carboxymethyl-Sepharose columns.
The Cationic peroxidase ELP is proved to be pure on SDS -
PAGE, and its molecular weight was 44 kDa. A study of
substrate specificity revealed the affinity of ELP to oxidize
some phenolic substrates in the order of ABTS > guaiacol > ophenylenediamine
> aminoantipyrene, while ELP had no
affinity towards ascorbic acid and o-dianisidine. The Km of
ELP for hydrolysis of H2O2 was 15 mM. The Km values of
electron donor substrates were also determined. The enzyme
had pH and temperature optima at pH 7.0 and a temperature of
40 °C, respectively. ELP was stable at 10 - 60 °C and unstable
above 60 °C. The thermal inactivation of ELP was
characterized by a rapid decline followed by a relative stability
in activity on exposure to heat. However, the thermal
inactivation of ELP was almost changed in the presence of
Ca2+ ions. Most of the different examined compounds and
Abstract
metal ions had partial inhibitory effects on ELP except for
Ca2+ which had a vital role in activation of the enzyme and
Mg2+ which had a slight activation effect.
Keywords: Calcium ions; Euphorbia tirucalli; Latex;
Peroxidase; Thermal inactivation.