Ribonucleosides and Ribonucleotides

Note Nucleoside and nucleotide are generic terns that include both ribo- and deoxyribo- fonns. Aso, ribonucleosides and ribonucleotides are here designated sinply as nucleosides and nucleotides (e.g., ribo-adenosine as adenosine), and deoxyribo-nucleosides and deoxyribonucleotides as deoxynucleosides and deoxynucleotides (e.g, deoxyribo adenosine as deoxyadeno-sine). Both fonns of nailing are acceptable, but the shortened names are more commonly used Ttynine is an exception ribotlynidine is used to describe its unusual occurrence in RNfY... 

These four bases are incorporated into deoxyribonucleosides and deoxyribonucleotides similar to the bases in ribonucleosides and ribonucleotides. The following structures show the common nucleosides that make up DNA. The corresponding nucleotides are simply the same structures with phosphate groups at the 5 positions. 

Natural cytokinins occur as free bases and as the ribonucleosides and ribonucleotides of -substituted adenine derivatives and also as constituents of particular molecular species of tRNA (18). 

Spectroscopic studies on periodate-oxidized ribonucleosides and ribonucleotides, which are used for affinity columns and for affinity labelling, inter alia, suggest that they exist in solution in hydrated and condensed forms, and not as the free dialdehydes (Scheme 4). Periodate-oxidized UDP has been used for affinity labelling of... 

M. Ghomi, A. Aamouche, H. Jobic, C. Coulombeau, O. Bouloussa (1997). In Biological Macromolecular Dynamics, (Ed.) S. Cusack, H. Buttner, M. Ferrand, P. Langan P. Timmins, p73-7S. Adenine Press, New York. Neutron inelastic scattering of p3nimidine nucleic acid bases, ribonucleosides and ribonucleotides. 

The remainder of the pathway consists of a series of isomerase and group tranx/er reactions (Fig. 11-26). These produce sugar phosphates ranging in size from the 3-carbon glyceraldehyde 3-phosphate to the 7-carbon sedoheptulose 7-phosphate. Also derived from ribulose 5-phosphate is ribose 5-phosphate, an essential component of ribonucleosides and ribonucleotides. The group exchange reactions are catalyzed by transaldolase... 

II. Influence of allopurinol and oxipurinol, their respective ribonucleosides and ribonucleotides on purine and pyrimidine biosynthesis in normal human skin fibroblasts. 

Unlike some other cytokinin metabolic enzymes with affinity for cytokinins and other purines, the three Phaseolus enzymes described here appear to recognize only trans-Z (and (diH)Z in the case of the O-xylosyltransferase). Thus, these enzymes are capable of distinguishing between the trans- and cw-isomers of Z as well as the free base and ribonucleoside forms. The fact that similar metabolic conversions of cis-Z do not occur underscores the importance of the enzymes in regulating cytokinin activity in relation to plant growth, which also involves only the trans-isomer of Z. Moreover, the inability of the enzymes to recognize structures other than the free base supports the central role of cytokinin free base as opposed to the ribonucleoside and ribonucleotide forms. 

The optimum conditions for periodate oxidation of ribonucleosides and ribonucleotides have been investigated. ... 

Ribonucleosides and ribonucleotides, and also reducing sugars, produce fluorescence (340 nm excitation, 470 nm emission maxima) when heated in acidic solution... 

Erlanger, B. F., Beiser, S. M. Antibodies specific for ribonucleosides and ribonucleotides and their reaction with DNA. Proc. nat. Acad. Sci. (Wash.) 52, 68-74 (1964). 

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