Insoluble reducing ends

Index Entries Cellulose cellobiohydrolase reducingsugar assays insoluble reducing ends solvent-accessible reducing ends. 

Reduced and neutralized cellulose preparations were assayed using the BC A assay as described for insoluble reducing ends using glucose as the calibration standard. 

Dissolve an oligosaccharide or glycan having a reducing end to be modified in 2 1 pyri-dine/glacial acetic acid (vol/vol) with a total reaction volume of 10-100 pi. If the carbohydrate initially is insoluble in the reaction solution, a prior dissolution in a minimal amount of DMSO or water can be done and then an aliquot transferred to the reaction medium. 

Unlike amylose, amylopectin, which is practically insoluble, is branched. On average, one in 20-25 glucose residues is linked to another chain via an al 6 bond. This leads to an extended tree-like structure, which— like amylose—contains only one anomeric OH group (a reducing end ). Amylopectin molecules can contain hundreds of thousands of glucose residues their mass can be more than 10 Da. 

In this article, we address the issue of determining substrate concentrations based on cellulose chain ends. Typical insoluble cellulose substrates were evaluated. Our study focused on the analysis of reducing ends, rather than non reducing ends, because of the relative ease with which reducing ends canbe detected and because of their importance with respect to reducing end-specific CBHs. The results are expected to be of relevance to those considering factors that dictate rates of CBH activity on typical cellulose substrates. 

Insoluble-Phase/Solvent-Accessible Reducing Ends... 

The removal of reduced end products will also be important, since any build up of these products will inhibit the forward reaction and may reach toxic concentrations. This removal can occur in two ways firstly, by precipitation of relatively insoluble reduced sulphur, and, secondly, diffusion away from the site of production and subsequent reoxidation. This division is not a simple one, however, since the two processes interact. The precipitation of pyrite, for instance, can be regarded as one step in the reoxidation of reduced sulphides. 

Most of the heavy-metal impurities present in 2inc salt solutions must be removed before the precipitation reaction, or these form insoluble colored sulfides that reduce the whiteness of the 2inc sulfide pigment. This end is usually achieved by the addition of 2inc metal which reduces most heavy-metal ions to their metallic form. The brightness of 2inc sulfide can be improved by the addition of a small amount of cobalt salts (ca 0.04% on a Co/Zn basis) (20). Barium sulfate [7727-43-7] formed in the first step is isolated and can be used as an extender. 

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