Graduate Thesis Or Dissertation
 

Identification of some esterases of the green bean (Phaseolus vulgaris L.)

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  • This investigation was conducted to differentiate the esterases in a water extract of freeze-dried green beans on the basis of inhibitor and substrate specificities. An attempt was made to classify these esterases according to the criteria used for animal esterases. Activity of the esterases was measured manometrically using the Gilson differential respirometer. Aqueous extracts of green beans were found to hydrolyze the acetyl, propionyl, and n-butyryl esters of glycerol, phenol, and 2-naphthol-6-SO₃Na. No hydrolysis of triolein or long-chain 2-naphthol-6-SO₃Na esters was noted, indicating the absence of lipases. A small amount of activity was observed when the choline esters served as substrates, but this was attributed to esterases other than cholinesterases. Optimum activity of the extract on triacetin, tripropion, tributyrin, phenyl acetate, and phenyl propionate occurred at pH 7.2. The effects of organophosphorus inhibitors, diethyl p-nitrophenyl thiophosphate, tetraethyl pyrophosphate, and diisopropylphosphorofluoridate, at concentrations ranging from 10⁻¹ M to 10⁻¹⁰ M on the esterase activity was studied. These data show that the green bean extract contains at least three esterases. One was resistant to certain organophosphorus compounds, suggesting similarity to animal arylesterases (aryl ester hydrolase, EC 3.1.1.2). Various concentrations of organophosphorus compounds inhibited the activity of the two other esterases. These were classified as carboxylesterases (carboxylic ester hydrolase, EC 3.1.1.1).
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