Purification and characterization of a novel p,p’-DDT dehalogenase from Aeromonas sp. strain MY1

Although dichlorodiphenyltrichloroethane (DDT) occupies a prominent position for its recalcitrance in the environment which led to its ban by the Stockholm Convention. This pesticide is still unregulated used in low and middle-income countries, which contributes to the global burden of this hazardous contaminant. In the recent time, biological approach has been proven to be effective and environmentally safer for the decontamination of the residual DDT. In this research, we reported a gel-purified p,p’-DDT dehalogenase from Aeromonas sp. strain MY1, revealing a single band with a molecular weight of approximately 37 kDa. The dehalogenase was unique for its capability to release chloride ions from p, p’-DDT substrate with optimum dechlorination activity at pH 8.0 and 35°C. The enzyme followed Michaelis-Menten’s kinetics and measurement of its initial velocities with various p,p’-DDT concentrations showed a Km of 27.05 μmol L-1 and Vmax of 476.19 μmol L-1 min-1. However, the enzyme lost its dechlorination activity in the presence of Ag2+ and Hg2+ This dehalogenase could pave a way for the effective decontamination of p,p’- DDT contaminated environment, suggesting its potentials for p,p’-DDT bio-cleansing applications

In Silico Site-Directed Mutagenesis of Ser11 and Lys107 on the Predicted 3D Structure of glutathione s-transferase from Acidovoras sp. KKS102

Bacterial glutathione s-transferases (GSTs) are known to have variety of functions in detoxification processes. It is familiar that this detoxification ability is achieved through the attack of the thiolate form of glutathione on the electrophilic centres of toxic compounds. Indeed, cytosolic glutathione s-tranferase from Acidovorax sp. KKS102 is now known to have a dehalogenation function. However, little is known about the specific aminoacids involved in this catalytic process. In this study, we investigated the effect of in silico site-directed mutagenesis of the evolutionarily conserved amino acids, Ser11 and Lys107, on the theoretical 3D structure of GST from Acidovorax sp. KKS102 (GST-KKS102) using Deep View/Swiss-Pdb Viewer. The substitution of Ser11, with aromatic amino acids, Tyr, Phe and Trp and positively charged amino acids, Arg, His and lys produced the greatest effect on the stability of the 3D structure of GST-KKS102. Indeed, at Lys107 position, substitution with nonpolar amino acids, Pro and Gly produced the highest structural stability effect on the theoretical 3D structure of the GST-KKS102. This in silico analysis suggests that Deep View rotamer scores could aid in planning in vitro site-directed mutagenesis studies in protein engineering.Keywords: Glutathione s-transferase, Acidovoras sp. KKS102, Site-directed mutagenesis, 3D structure, Ser11, Lys10

Changes in catalase activities during malting of some improved Nigerian sorghum grain varieties

The catalase activities of ten germinating improved sorghum varieties were monitored over a 4-day period to determine the effect of malting on them. This was done using standard methods that involved catalase assay at the appropriate experimental intervals. Results obtained showed that the different varieties of sorghum differed in their expression of catalase, a difference that was also reflected across the different stages of the malting process. The highest overall catalase activity (20.54 ± 0.74 U) was given by variety SK5912 after 72 hours of germination followed in second place by that from variety Nafelen (18.65 ± 0.99 U) obtained after steeping. The third and fourth highest value (17.88 ± 1.24 U and 17.08 ± 1.64 U) were given by KSV8 and Boboje after 72 and 48 hours of germination respectively. These values are probably indications that no single stage of malting was best for catalase expression among all the varieties. However, the fact that most of them (varieties ICSV 400, SK5912 and KSV 8, CSRO2 and ICSV III) all expressed their highest catalase activities after 72 hours of germination showed that 72 hours is probably the best germination stage for the elicitation of catalase among sorghum grains. The next best stage should be after 48 hours during which point three varieties (Boboje, NRL 3 and KAT 487) had their highest catalase activities. As a unity, all the sorghum varieties had their lowest catalase expression after 24 hours of germination, followed by those obtained after 96 hours germination.Keywords: catalase, sorghum, malting, peroxidase, cereal enzyme