Purification and characterisation of a carboxylesterase from the latex ofSynadenium grantii Hook, ‘f’

The latex ofSynadenium grantii was found to contain esterolytic activity. Polyacrylamide gel electrophoretic study coupled with substrate and inhibitor specificity studies revealed the presence of multiple forms of carboxylesterases and cholinesterases in the latex. One of the carboxylesterases of the latex was purified by acetone fractionation, carboxymethyl-Sephadex chromatography and Sepharose-6B gel filtration. The homogeneity of the enzyme was established by polyacrylamide gel electrophoresis, isoelectric focussing and sodium dodecyl sulphate-polyacrylamide gel electrophoresis. The enzyme consists of a single polypeptide chain with a molecular weight of 14,000. The amino acid analysis of the purified enzyme revealed that it contained a greater number of neutral and acidic, compared to basic amino acid residues. The isoelectric pH of the enzyme was found to be 4.0. The enzyme was a glycoprotein as revealed by periodic acid Schiff-staining technique. Studies with different organophosphate and carbamate inhibitors showed that this enzyme was sensitive to organophosphates. The product inhibition studies with this enzyme showed linear competitive inhibition with acetate and linear non-competitive inhibition with 1-naphthol.     

Temperature effects on cholinesterases from rat brain capillaries

The activities of acetylcholinesterase (ACHE) and butyrylcholinesterase (BuChE) in rat brain capillaries were measured as a function of temperature. Arrhenius plots of the data revealed that AChE exhibits a biphasic Arrhenius plot with a distinct break (transition temperature) at about 15.2 kcal/mol. In contrast, BuChE did not show evidence of discontinuity. BuChE showed an activation energy higher than that of AChE in the physiological range of temperature. These data suggest a lack of lipid-protein interaction in the case of BuChE. Although the possibility exists that BuChE is weakly anchored to the membranes, our results indicate that BuChE is not bound, at least significantly, to cellular membranes in brain capillaries as is ACHE.