Synthesis and Degradation of Polysaccharides

Because, under any set of conditions, phosphorylase catalyzes synthesis and degradation of polysaccharides, equilibrium is eventually reached. The value of the ratio [inorganic phosphate]/[D-glucosyl phosphate] at equilibrium is remarkably constant over a wide range of concentration of polysaccharide, but varies with pH, because both substances can ionize it varies from 5.7 at pH 6 to 2.7 at pH 7.6. 

The continuing interest of Bourne in the chemistry of polysaccharides and associated enzymes originated from the work of Haworth and Peat directed towards the enzymic synthesis and degradation of starch. The impetus for this work was given by the discovery, made by C. S. Hanes in 1940, that a phosphorylase isolated from the potato and pea effects the synthesis, from D-glucosyl phosphate, of starch, later shown (by Haworth, Heath, and Peat) to be amylose. In his first paper (with Haworth and Peat) in 1944, Bourne described the isolation of the Q-enzyme which, in conjunction with phosphorylase, effects the conversion of D-glucosyl phosphate into the major component of whole starch, namely, amylopectin. He had discovered the Q-enzyme in a fraction discarded by previous workers. Already, the quintessence of his mind was revealed in this work meticulous attention to detail, and perception of essentials. 

The Enzymic Synthesis and Degradation of Starch. Part VIII, The Use of Mixtures of P- and Q-Enzymes in the Synthesis of Starch-type Polysaccharides, S. A. Barker,... 

A. The Measurement of Isotopes. B. The Synthesis and Degradation of Labeled Compounds (Including. Application to Metabolic Studies) Monosaccharides and Polysaccharides Citric -Acid Cycle Intermediates Glycolic, Glyoxylic and Oxalic Acids Purines and Pyrimidines Porphyrins Amino. Acids and Proteins Steroids Methylated Compounds and Derivatives Sulfur Compounds Fatty. Acids Phospholipids Coenzymes lodinatftd Compounds Intermediates of Photosynthesis 0 -Labeled Phosphorus Compound. . 

The rate of synthesis, or degradation, of amylose depends on the degree of polymerization of the polysaccharide the action is faster on the species of lower molecular weight. It is thought that inactive enzyme—substrate complexes can form between phosphorylase and internal sections of D-glucosidic chains, and the result of this is an effective diminution in the concentration of enzjune free to attack chain ends. As the inactive complexes are more likely to form with the longer molecules of amylose, the rate of reaction decreases with increasing molecular size of the polysaccharide. 

Because of their great biological importance, starch and glycogen have been the subject of intensive investigation for many years. It is, therefore, no accident that there should be more information available at present concerning their mechanisms of synthesis and degradation than about any other natural polysaccharide. 

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