Identification of carboxylesterase activities of commercial triacylglycerol hydrolase (lipase) preparations

The carboxylesterase activities of 34 commercial lipase preparations (CLP), from bacterial, fungal, and mammalian sources, were characterized by isoelectric focusing and nonreducing SDS‐PAGE followed by alpha‐naphthyl acetate zymography. Substantial differences in both the numbers of stained proteins and the enzymatic activity banding patterns were seen, even among preparations from the same organism, indicating a great heterogeneity of enzyme activities in commercial lipase preparations. CLP displayed between 1 and 16 carboxylesterase activity bands of discrete isoelectric points, many of which were not detected by silver stain. Most carboxylesterase bands did not display lipase activity: although 26 CLP contained carboxylesterase bands with isoelectric points identical to previously documented lipase activity bands, there were many more carboxylesterase bands than lipase bands. Conversely, twenty CLP lacked carboxylesterase activity at one or more isoelectric points previously shown to exhibit lipase activity. Only in 11 CLP did all electrofocused lipase bands also display carboxylesterase activity. Few carboxylesterase bands (0—4) were detected after nonreducing SDS‐PAGE and alpha‐naphthyl acetate zymography. About half of these were undetectable by silver stain, suggesting high activities. The range of apparent molecular mass (AMM) of active carboxylesterases was 24—67 kDa, lower than the AMM of protease activities present in these lipase preparations, indicating that most esterase activities were not caused by the proteases in the preparations. Seven preparations demonstrated carboxylesterase activity at the same AMM as proteases.