Reducing End Groups

To determine the presence of RGase in the various prq>arations isolated RG was treated with these products. After incubation, the formation of reducing end-groups was measured by the DNS-method. 

The structure of amylopectin according to Meyer is shown in Fig. 65. The single reducing end group is indicated by A all other terminal units are attached at the 1-position only. 

Amylose is thus extremely susceptible to degradation in the presence of hydroxyl ion. Two mechanisms may be involved (1) a stepwise degradation caused by the reducing end-group s undergoing enolization followed by degradation to acidic products (this must occur in the presence or absence of oxygen), and (2) a random, catalytic, hydrolytic scission of 4—>l-a-D... 

During secondary liquefaction at 95 C or 90 C, a r id reduction in viscosity was observed. At 90 C, the viscosity reduction was monitored over time with a Nametre viscometer. The results demonstrated there was a r id reduction in viscosity to 400 centipoise x gm/cm by 7 minutes into secondary liquefaction (Figure 6). The action patterns of the liquefied starches following secondary liquefaction demonstrated the characteristic cyclodextrin action pattern at both temperatures. DE values were < 1.0 indicating the absence of reducing end-groups consistent with the mechanism of a CGTase. 

Assuming one reducing end-group. Reducing power of sugar recovered after hydrolysis in N HC1 for 1 hr. c Hydrolysis by 0.1 N HC1 for 1 hr. 

Doner, L. W. and Irwin, PL. 1992. Assay of reducing end-groups in oligosaccharide homologues with 2,2 -bicinchoninate. Anal. Biochem. 202 50-53. 

Cx enzymes occur in multiple forms in most cellulose systems, and they appear to be different enzymes with different relative activities on a number of cellulose substrates. It was always possible, then, but not necessarily likely, that a completely different Cx system was being synthesized in each case and that this would account for the difference in synergism. This possibility was excluded, however, when it was found that each Cx system was identical in terms of CM-cellulase activity in each case the number of reducing end groups produced per unit decrease in viscosity was the same. 

The reducing end groups in cellulose are the only naturally occurring carbonyl functionalities in this material. Cellulose from Acetobacter xylinum [43] contains an amount of carbonyl groups which corresponds approximately to the number of reducing end groups, and can be considered as rather genuine material. 

Reducing end groups can be readily further oxidized to the corresponding aldonic acids. 

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