Galactosiduronic acid

Fig. 4. Molecular mass distribution of Fraction A purified on Concanavalin A -cellulose on Superose 12 column. Buffer - 0.05 M phosphate, pH 7.0, 0.15 M NaCl, fraction size 0.5 ml/min. Exopolygalacturonase activity determined with penta(D-galactosiduronic) acid pH 5.0 and pH 3.8 (0—0)-...

The inicial reaction rates of exopolygalacturonase forms distinguished on the base of their pH optima on substrates with various degree of polymerization [(GA)j - di(D-galactosiduronic) acid, (GA)5 - penta(D-galactosiduronic) acid. 

The difference in the effect of various endo-D-galacturonanases on oligomeric substrates [in particular, the difference in the rate of degradation of tri(D-galactosiduronic acid) and in the action pattern toward the tetrasaccharide] indicates, however, that it is not the substrate, but rather, the properties of the enzyme (in particular, the character of its active center) that constitute the determining factor. 

The tri(D-galactosiduronic acid) 3-glycoside of L-galactonolactone is resistant to the activity of these enzymes. Penta(D-galactosiduronic acid) (1) whose reducing-end unit had been oxidized by periodate was split by the enzyme of Acrocylindrium to oxidized dimer and tri(D-galactosiduronic acid) (3).119... 

The activity of tomato endo-D-galacturonanase follows action pattern B (see Scheme 1), which is characterized by an alternative cleavage of tetra(D-galactosiduronic acid) and by a relatively rapid degradation of trisaccharide.128 In the tetrasaccharide, bond 1 is split faster than bond 2. Bond 3 is not broken by the enzyme. Both the reduced and oxidized tetra(D-galactosiduronic acid) derivatives are hydrolyzed by this enzyme at bond 2. 

Action pattern C (see Scheme 1) was observed with the extracellular endo-D-galacturonanase produced by Erwinia caro-tovora.123 It differs from the first two types in a specific hydrolysis of penta(D-galactosiduronic acid) (1) to trisaccharide and disaccharide, and in having only two alternative ways for cleavage of hexa-saccharide. Both bonds are split in the trisaccharide 3. The pentasaccharide is split five times faster than the tetrasaccharide. 

For endopectate lyases, the rate of cleavage of glycosidic bonds and the affinity of the enzyme for the substrate depend on the chain length,240,241 as with endo-D-galacturonanase. The frequency of splitting of bonds 2 and 3 in tetra(D-galactosiduronic acid) is different. Endopectate lyase of Bacillus polymyxa splits240 bond 3 1.4 times faster than bond 2. 

Analysis of the products of splitting of esterified tetra- through hexa-(D-galactosiduronic acid) showed pectin lyase to be unable to split the first and the second bonds, starting from the reducing end of... 

Action0 of Pectin Lyase on Methyl Esters of Tetra-, Penta-, and Hexa-(D galactosiduronic Acids)... 

Deoxy-L-threo-hexos-5-ulosuronic acid (10), the product of the action of oligo-D-galactosiduronate lyase, shows no absorption at 235 nm therefore, its activity is estimated on the basis of the decrease in ultraviolet absorption at this wavelength, using unsaturated di(D-galactosiduronic acid) as the substrate. 

---