الفهرس 
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Abstract
The interest in α-amylases production from unconventional inexpensive plant sources is very essential due to their wide industrial applications especially food processing and medical fields, α-amylases displayed marked active over a wide range of temperature and pH, and possess broad substrate specificity and stability under variable conditions, consequently this study has focused on the eligibility of Euphorbia tirucalli latex which possessed a suitable level of α-amylases to be a good inexpensive starting material for α-amylases production. The selection of the plant latex was done due to its consideration as a defense mechanism which means it should has strong characters. The findings obtained can be summarized in the following:
1- α-Amylases activity level was quantitatively determined in Euphorbia tirucalli latex to be 131.7 units mg-1. The results indicated that Euphorbia tirucalli latex could be potentially a good source for production of α-Amylase.
2- E. tirucalli α-Amylases AI, AII and AIII were purified to homogeneity as judged by polyacrylamide gel electrophoresis. The purification scheme involved extraction, chromatography on DEAE-Sepharose and gel filtration using Sephacryl S-200. The purified E. tirucalli α-Amylases AI, AII and AIII have specific activities of 175.3, 87.22 and 64.92 units mg-1 protein, with fold purification 1.33, 0.66 and 49.3 over the crude extract, respectively.
3- The molecular weights of E. tirucalli α-Amylases AI, AII and AIII have been found to be 23, 27 and 40 kDa, respectively as calculated from the calibration curve of Sephacryl S-200 column. These values were confirmed by SDS-PAGE, where the three enzymes migrated as single protein bands suggesting that AI, AII and AIII were monomeric.
4- It is clearly seen that the E. tirucalii α-amylase AI has the highest activity. So, the characterization of this enzyme was done.
5- The effect of pH on E. tirucalii α-amylase AI activity revealed that AI had a pH optimum at 6.0.
6- The effect of temperature on E. tirucalii α-amylase AI indicated that AI had a temperature optimum at 50 ̊ C. Heat stability studies on E. tirucalii α-amylase AI revealed that the enzyme was stable up to 50 ̊ C, followed by a decrease in the stability upon increasing the temperature where it lost about 30 % and 60% of its activity at 60and 80 ̊ C, respectively, which means that AI enzyme is moderately thermostable.
7- The effect of different metal cations on the activity of E. tirucalii α-amylase AI revealed that the Ca+2 had stimulatory effects on AI activity, while Ni2+, Ba2+, Zn2+, Cu2+, Fe2+ , Mn2+ and Hg2+ had different inhibitory effects.
8- The inhibitory effect of different compounds for E. tirucalii α-amylase AI indicated that All the metal chelators at the concentration of 2 mM caused inhibition effect for E. tirucalii α-amylase AI like EDTA caused a strong inhibition for the enzyme (77% inhibition), while sodium citrate and sodium oxalate caused partial inhibitory effects (44.8% and 43.8% inhibition, respectively). For inhibitors, namely PMSF (serine inhibitor) and 1,10 phenanthroline (metal inhibitor) caused slight inhibitory effects on -amylase AI (12% and 29%, respectively), while the enzyme was strongly inhibited by p-HMB (64% inhibition).
9- The substrate specificity of E. tirucalii α-amylase AIwas determined for a number of substrates. The affinity decreased in the order of amylopectin > Potato soluble starch > β – Cyclodextrin. On the contrary, it has no activity toward -cyclodextrin.
10- Km values of E. tirucalii α-amylase AI were determined for Starch and amylopectin and were found to be 0.588 and 0.34 mg/ml, respectively.