N alpha- and N epsilon-D-galacturonoyl-L-lysine amides: properties and possible occurrence in plant cell walls.
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 1H and 13C NMR spectroscopy to be tri- and tetra-alpha-(1-->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-[6-14C]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 [14C]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.
Perrone
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Edinburgh Cell Wall Group, University of Edinburgh, U.K.
Hewage
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Sadler
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Fry
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D000577:Amides / Q000138:chemical synthesis* / Q000378:metabolism; D002240:Carbohydrate Sequence; D002473:Cell Wall / Q000378:metabolism; D006001:Glycoconjugates / Q000138:chemical synthesis* / Q000378:metabolism; D006603:Hexuronic Acids / Q000138:chemical synthesis* / Q000378:metabolism; D018551:Solanum lycopersicum / Q000378:metabolism*; D008239:Lysine / Q000031:analogs & derivatives* / Q000378:metabolism; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D018724:Spinacia oleracea / Q000378:metabolism*
D000577:Amides; D006001:Glycoconjugates; D006603:Hexuronic Acids; C007819:galacturonic acid; D008239:Lysine