الفهرس 
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Abstract
This study aimed to determine tyrosinase activity in some C3 plants (Lupinus termis, Pisum sativum, Cucurbita pepo, Cicer arietinum and Helianthus annus), then choosing the plant extract with the highest enzyme activity to be studied in the present investigation and this plant was Cucurbita pepo. The enzyme activity was assayed under different physiological treatments such as some hormones like indol acetic acid, gibberellic acid and epi-brassinolid. The activity of the enzyme was also assayed under the effect of some azole compounds such as uniconazole and 3-amino-1,2,4-tiazole and some thiols such as cysteine and mercaptoethanol. The activity was assayed under the effect of the heavy metals (AlCl3, CuCl2 and ZnCl2) that inhibited the enzyme activity and partial alleviation of the toxic effect by using ammonium sulphate or benzyl adenine. The activity was tested under the effect of four algal extracts Corallina mediterranea, Hypnea musciformis, Pterocladia capillacea and Ulva fasciata. The activity of the extracted enzyme was assayed under different treatments such as some amino acids, some aldehydes, urea, succinic acid, some vitamins, some organic acids, some phenolic compounds, some anions and some cations and some plant extracts such as Cinnamomum zeylanicum, Zingiber officinale, Capsicum annuum, Euphorbia helioscopia, Euphorbia peplus, Beta vulgaris var cicla, Rumex dentatus, Malva parviflora and Solanum nigrum and kiwi fruit. Tyrosinase was purified using ammonium sulphate (65%) and Sephadex-G75. The specific activity of the purified enzyme was estimated during the purification steps. The enzyme physicochemical and kinetic properties were estimated such as temperature, pH, incubation time and thermal stability, Km and Vmax values were also estimated. The enzyme was immobilized using different carriers including physical binding, chemical binding, covalent binding and entrapment, The immobilized enzyme by entrapment using calcium alginate has the highest activity. Physicochemical and kinetic properties of immobilized tyrosinase were studied such as temperature, pH, thermal stability and Km and Vmax values.