An esterase from Escherichia colithat is a member of the hormone-sensitive lipase (HSL) family was overproduced, purified and characterized. It is encoded by the ybaCgene and composed of 319 amino acid residues with an Mr of 36038. The enzymic activity was determined by using various p-nitrophenyl esters of fatty acids as a substrate at 25 °C and pH 7.1. The enzyme showed hydrolytic activity towards substrates with an acyl chain length of less than 8, whereas it showed little hydrolytic activity towards those with an acyl chain length of more than 10. In addition, it showed little hydrolytic activity towards trioleoylglycerol and cholesterol oleate. Determination of the kinetic parameters for the hydrolyses of the substrates from C2 to C8 indicates that C4 and C5 substrates are the most preferred. Close agreement between the Mr determined by SDS/PAGE (37000) and column chromatography (38000) suggests that the enzyme exists in a monomeric form. It is an acidic protein with a pI value of 4.1. The far-UV CD spectrum suggests that its helical content is 26.1%. Comparison of the amino acid sequence of this enzyme with those involved in the HSL family allows us to propose that Ser165, Asp262 and His292 constitute the catalytic triad of E. coliesterase.

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