N alpha- and N epsilon-D-galacturonoyl-L-lysine amides: Properties and possible occurrence in plant cell walls

P Perrone, C M Hewage, I H Sadler, S C Fry

Research output: Contribution to journalArticlepeer-review

Abstract

Three representatives of a novel class of amide (isopeptide) glycoconjugates have been synthesised: N alpha-D-galacturonoyl-L-lysine and N epsilon-D-galacturonoyl-L-lysine and,N epsilon-D-polygalacturonoyl-L-lysine. Galacturonoyl-lysine amide bonds were labile in 2 M trifluoroacetic acid at 120 degrees and in alkali, but relatively stable in cold acid. The amide bonds were resistant to digestion by Driselase, Pronase and trypsin. The polysaccharide backbone of N epsilon-D-polygalacturonoyl-L-lysine was hydrolysed by Driselase to yield two major ninhydrin-positive compounds which were shown by H-1 and C-13 NMR spectroscopy to be tri- and tetra-alpha-(l --> 4)-D-galacturonoyl-L-lysines. To investigate the possible natural occurrence of N-galacturonoyl isopeptide bonds, we fed cell-suspension cultures of spinach and tomato with D-[6-C-14]glucuronic acid, which radio-labels pectic polysaccharides. The radioactive cell walls were digested with, sequentially, Driselase, mild acid, and proteinases. On electrophoresis at pH 2.0, several of the radioactive digestion-products were cathodic. Some of the cathodic products yielded [C-14]galacturonic acid upon complete acid hydrolysis. The existence of these products is compatible with the presence of novel N-galacturonoyl isopeptide bonds, which could serve as cross-links in plant cell walls. (C) 1998 Elsevier Science Ltd. All rights reserved.

Original languageEnglish
Pages (from-to)1879-1890
Number of pages12
JournalPhytochemistry
Volume49
Issue number7
Publication statusPublished - Dec 1998

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