engleski

Isolation and properties of the guinea-pig esterases hydrolyzing esterified monosaccharides

Background and purpose: It has been already reported that the rabbit serum is a rich source of esterase activities with specificity for carbohydrate esters, as demonstrated among other substrates by regioselective hydrolysis of radiolabelled methyl 2, 6-di-O-pivaloyl-a-D- glucopyranoside (2, 6-DP). Native serum and the main isolated esterase primarily hydrolyzed the acyl group located on a primary 6-hydroxyl group in the sugar ring. On the other hand, it is known that the guina-pig serum is also a rich source of esterases, but a specificity toward carbohydrate substrates has not been studied before. Materials and methods: The guinea-pig serum was submitted to column chromatography on DEAE- Sepharose CL-6B. Three peaks hydrolyzing 2, 6-DP, used as a substrate, were isolated. The course of hydrolyses was followed using a thin layer chromatography, 14C-labelled 2, 6-DP as a substrate and expected 14C-labelled hydrolysis products as references. The measurment of radioactivities associated with products formed indicated the extent and preferred direction of hydrolysis. Results: Three peaks with esterase activities were located by column chromatography of the guinea-pig serum. The first one (Peak I) hydrolyzed 2, 6-DP in a regioselective manner to produce mainly 6- monopivalate (6-MP). The second one with lower specific activity (Peak II) regioselectively produced 2-monopivalate (2-MP), and the third one with very low specific activity (Peak III) showed no preference for a particular pivaloyl and gave a mixture of a 2-MP and 6-MP. Preliminary characterization of isolated Peaks was attemped by using a series of inhibitors specific for various possible types of esterases. Thus, POX, BNPP, eserine, EDTA and HgCl2 indicated that all three Peaks may belong to a category of carboxylesterases. Conclusion: The guinea-pig serum is a good source of esterase activities catalyzing the hydrolysis of acylated carbohydrates. These activities could be separated by chromatography. It is found that each of these activities catalyses the hydrolysis of acyl groups at different rates. Two of them caused regioselective deacylation, but the direction of hydrolysis differed. These results may be of great potential use in regioselective transformations of sugars in mild reaction conditions.

guinea-pig esterases ; monosaccharides

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