Abstract
Several Upases and phospholipase A2 (PLA2) were chemically modified with ethyl caprylimidate, the capryl ester of p-hydroxyphenyldimethylsulfonium methyl sulphate (C8-DSP-ester), the capryl carbonate of p-hydroxyphenyldimethylsulfonium methyl sulphate (C8-DSP-carbonate) and polyethylene glycol monomethyl ether activated with p-nitrophenyl chloroformate (pNP-MPEG). PLA2 could be easily modified to high degrees, whereas modification of lipases was less efficient. The poor modification with the C8-DSP-ester, C8-DSP-carbonate, and pNP-MPEG can be explained by hydrolysis of the reagents by the lipases and by impurities present in the crude lipase preparations. Purification of the lipases decreases the hydrolysis rate of the reagent, but the enzymatic hydrolysis of the reagent remains considerable. For purified Candida rugosa lipase the hydrolysis of pNP-MPEG is slow enough to give a relatively high degree of modification when reacted with this reagent. The degree of modification for Candida antarctica lipase B and Staphylococcus hyicus lipases could be enhanced by increasing the pH of the modification reaction and addition of the reversible inhibitor, 2,4-dichlorobenzeneboronic acid.
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