Galacturonic acid isolation

The substrate for HGA synthesis is UDP-D-galacturonic acid (UDP-GalA) (81). UDP-GalA has been isolated from plants (59) and several pathways for its synthesis in planta have been reported (31). In vitro studies on pectin biosynthesis have been hampered since radiolabeled UDP-galacturonic acid is not commercially available. Previous researchers have used several... 

Neufeld, E.F. and Feingold, D.S. (1961) Isolation of uridine diphosphate-galacturonic acid from seedlings of Phaseolus aureus. BiochimBiophysActa, 53 589-590. 

Pectins from different tissue zones, namely epidermis, the outer parenchyma, the parenchyma of the Ccirpels zone, the carpels and the core line, were isolated firom alcohol-insoluble solids (AIS. In both zones of parenchyma, the cell-wall material represented about 80% of the total cell-wall material from the whole fruit. The pectins from the outer parenchyma accounted for 70% of the total. However, there was no change in galacturonic acid concentration. The enzymatic solubilisation of tissues or AIS was higher in the parenchyma zones than in the others. Nevertheless, the depolymerisation of the soluble pectins from parenchyma zones with an endopolygacturonase required the action of pectin methylesterase. The depoiymerisation of pectins from the other zones, however, did not. 

Oligosaccharides consisting of galacturonic acid and rhamnose with dp 3-5 and a series of 1,4 linked galacturonic acid oligosaccharides of dp 4-10 were isolated. 

Characteristics of fraction I. The carbohydrate content of Fraction I was 84.4 %, in which the main component is D-galacturonic acid (71 %). Consequently, the polysaccharide is of a pectic type. The neutral sugars accounted for 13.4 % and according to their qualitative composition (Table 2) they correspond to the composition of pectin, isolated from sunflower heads (18). It is worth noting the high content of L-arabinose and D-galactose, compared with the other monosaccharides. The protein content was 7.8 %. 

Immunoactive polysaccharides, containing galacturonic acid have been isolated from different plants and cell suspension culture liquids (2,4,19-22). 

The r2 isolate of Fusarium oxysporum f. sp. radicis-lycopersici (FORL) produced several pectic enzymes that differ in substrate preference, reaction mechanism, and action pattern. We have detected three forms that have lyase activity, an absolute requirement for calcium, and pis of 9.20, 9.00 and 8.65. The two most alkaline forms had a weak preference for pectin whereas the other was more active on pectate. The three lyases were produced when the fungus grew on pectin and on restricted galacturonic acid (data presented in the "XV Congreso Nacional de Microbiologia" [21] and sent for publication). 

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