Monosaccharides, metabolic labeling

Table 1 Azide- and aUcyne-bearing monosaccharides used for metabolic labeling of glycans...

Physical or chemical modification of a substrate may additionally selectively affect transformation or uptake Keil and Kirchman (1992) compared the degradation of Rubisco uniformly labeled with 3H amino acids produced via in vitro translation to Rubisco that was reductively methylated with 3H-methane. Although both Rubisco preparations were hydrolyzed to lower molecular weights at approximately the same rate, little of the methylated protein was assimilated or respired. The presence of one substrate may also inhibit uptake of another, as has been demonstrated for anaerobic rumen bacteria. Transport and metabolism of the monosaccharides xylose and arabinose were strongly reduced in Ruminococcus albus in the presence of cellobiose (a disaccharide of glucose), likely because of repression of pentose utilization in the presence of the disaccharide. Glucose, in contrast, competitively inhibited xylose transport and showed noncompetitive inhibition of arabinose transport, likely because of inactivation of arabinose permease (Thurston et al., 1994). 

From this brief survey, it is seen that there were few features of carbohydrate metabolism in plants that escaped Hassid s touch, and much that we now know about the role of sugar nucleotides in the interconversion of carbohydrates in plants is a direct result of his persistent effort. From the incorporation of labelled precursors into monosaccharides, to the conversion of the monosaccharides into their glycosyl phosphates, to the action of the pyrophosphorylases in the synthesis of glycosyl esters of nucleoside pyrophosphates, to the interconversion of the resulting sugar nucleotides, to the polymerization of the activated monosaccharides to yield disaccharides and the homopolysaccharides, and, finally, to the modification of the polysaccharides by methylation—in summary, to almost every aspect... 

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. . 

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