Analysis of pectin structure part 1 - Analysis of different de-esterification mechanisms for pectin by enzymatic fingerprinting using endopectin lyase and endopolygalacturonase II from A-niger

A series of pectins with different distribution patterns of methyl eater gr oups was produced by treatment with either plant (p-PME) or fungal pectin m ethyl esterases (f-PME) and compared with those obtained by base catalysed de-esterification. The products generated by digestion of these pectins wit h either endopectin lyase (PL) or endopolygalacturonase II (PG II) from Asp ergillus niger were analysed using matrix assisted laser desorption ionisat ion mass spectrometry (MALDIMS) and high-performance anion-exchange chromat ography with pulsed amperometric or UV detection (HPAEC-PAD/UV). Time cours e analysis using MALDIMS was used to identify the most preferred substrate for each enzyme. For FL, this was shown to be fully methyl esterified HG wh ereas for PG II, long regions of HG without any methyl esterification, as p roduced by p-PME was the optimal substrate. The blockwise de-esterification caused by pPME treatment gave a decrease of partly methylated oligomers in PL fingerprints, which did not effect the relative composition of partly m ethylated oligomers. PG II fingerprints showed a constant increase of monom ers and oligomers without any methyl ester groups with decreasing degree of esterification (DE), but almost no change in the concentration of partly m ethylated compounds. PL fingerprints of f-PME and chemically treated pectin s showed decreasing amounts of partly methyl esterified oligomers with decr easing DE, together with a relative shift towards longer oligomers. PG II f ingerprints were characterised by an increase of partly methylated and not methylated oligomers with decreasing DE. But differences were also seen bet ween these two forms of homogenous de-esterification. Introduction of a cer tain pattern of methyl ester distribution caused by selective removal of ce rtain methyl ester groups by f-PME is the most reasonable explanation for t he detected differences. (C) 2000 Elsevier Science Ltd. All rights reserved .