Modeling of enzymatic activity of free ß-glucosidase from palm weevil, Rhynchophorus palmarum Linn. (Coleoptera: Curculionidae) larvae: Effects of pH and temperature.

Palm weevil, Rhynchophorus palmarum L., is an important pest of palm trees (Elaeis guineensis) around the tropical regions. Characterization of their digestive enzymes could be an important stage to develop appropriate pest control strategies. Study of these enzymes could also be of interest in different biotechnological applications. Among digestive enzymes, there is ß-glucosidase which hydrolytically catalyzes the ß-glycosidic linkage of glycosides. In the present work, the catalytic activity of ß-glucosidase in the digestive juice of last larval instar of R. palmarum L. (Rpbgl) has been investigated using p-nitrophenyl-ß-D-glucopyranoside (pNPG) as substrate. The "classical" physico-chemical properties for purified Rpbgl have been determined by the help of enzymatic activity modeling. Thus, the values of (325.4 ± 0.2) K, 5.28 ± 0.07 and (37.9 ± 0.6) kJ mol-1 were obtained for optimum temperature, optimum pH and activation energy, respectively. The pK values for enzyme-substrate complex are 4.25 ± 0.07 and 6.20 ± 0.07 for nucleophile and the proton donor, respectively. Enzyme kinetics study was also performed and the values of (127 ± 6) U mg-1 and (0.78 ± 0.08) mM were obtained for Vmax and Km, respectively. Using the Equilibrium model (EM), the thermal inactivation data were analyzed. ΔHeq, Teq, ΔGinact∗ and ΔGcat∗ were found to be (222 ± 4) kJ mol-1, (323.0 ± 0.1) K, (101.9 ± 0.2) kJ mol-1 and (53.37 ± 0.02) kJ mol-1, respectively. These results show that Rpbgl is less stable with a narrow temperature tolerance compared to other ß-glucosidases.

Effect of boiling time on chemical composition and physico-functional properties of flours from taro (Colocasia esculenta cv fouê) corm grown in Côte d'Ivoire.

Taro (Colocasia esculenta cv fouê) corm was subjected to different boiling times and the changes in chemical composition and physico-functional properties were investigated using standard method. The change in boiling time led to a significant (P < 0.05) reduction in the moisture, reducing sugars, total sugars, crude fat, crude fibre, total phenolic compound contents and iodine affinity of starch, whereas the total carbohydrate content, water absorption capacity, water solubility index, paste clarity and foam capacity increased significantly (p < 0.05). The crude protein and total ash contents of the flours from taro corm were not affected significantly (p < 0.05) by the change in boiling time. Taro corm flours exhibited highest total carbohydrate, crude fibre, total ash contents, water absorption capacity, iodine affinity of starch and lowest crude protein and fat contents, foaming capacity and water solubility index. Principal component analysis showed that flours from taro corm boiled during 20 min and 15 min were located at the left of the score plot, while flours from raw and boiled taro corm during 10 min had a large positive score in the first principal component.

Purification, kinetic properties and physicochemical characterization of a novel acid phosphatase (AP) from germinating peanut (Arachis hypogaea) seed.

Acid phosphatase activity was detected in peanut (Arachis hypogaea) cotyledons during germination. Four (4) to six (6) days of germination was the meantime corresponding to maximum hydrolytic activity of this enzyme. The understanding of the role of acid phosphatase activity during germination led to purify this enzyme by successive chromatography separations on DEAE-Sepharose CL-6B, Sephacryl S-100 HR and Phenyl-Sepharose HP to apparent homogeneity from germinated peanut cotyledon five days old. This enzyme designated peanut cotyledon acid phosphatase (AP) had native molecular weight of 24 kDa by gel permeation. SDS-PAGE of the purified acid phosphatase resolved a single protein band that migrated to approximately 21.5 kDa. Thus, this acid phosphatase likely functions as a monomer. The enzyme had optimum pH (5.0) and temperature (55 degrees C), and appeared to be stable in the presence of anionic, cationic and non-ionic detergents. Substrate specificity indicated that the purified acid phosphatase hydrolyzed a broad range of phosphorylated substrates. However, natural substrates such as ADP and ATP were the compounds with highest rate of hydrolysis for the enzyme. Moreover, the purified acid phosphatase exhibited phytase activity. These results showed that this enzyme played a peculiar role during germination, notably in reducing the rate of phytic acid, an antinutritional substance contained in peanut seed.