Ribose/phosphate reaction chemicals

Finally, Buchtal et al. (1949) investigated whether chemical changes take place in F-actomyosin when the threads shrink. Threads of F-actomyosin and also of L-myosin were found to contain, after treatment with 2 X 10 M ATP followed by 7-12 washings, a content of phosphate, adenine and ribose three to five times greater than before. The relative amounts of the different phosphate reactions (c/. Section III, 4a) are not appreciably altered from those already present. The effect is as specific for ATP as shrinkage and contraction, but it probably has no direct connection with the fundamental process of contraction since it also occurs when actomyosin and L-myosin are in the dissolved state (c/. Section III, 5d). 

RNA carries out its enzymic roles with many fewer chemical resources than its protein counterparts it has a ribose-phosphate backbone (Chap. 3), with four rather similar heterocyclic nucleobases, plus attendant water molecules and metal ions. They carry out the water-elimination condensation reactions in splicing certain classes of introns (Chap. 7) and in the site-specific cleavage and ligation of small replicating RNA circles in some species of organism. 

PP-Ribose-P is the most important ribose phosphate donor for purine metabolism (see Chapters 7, 8) and participates in several important reactions of pyrimidine metabolism (Chapters 11, 12) it also transfers this group to a number of other acceptors (Chapter 5). In the course of studies of purine ribonucleotide biosynthesis, a product of the reaction of ribose-5-P and ATP was isolated and eventually identified as 5-phosphoribosyl 1-pyrophosphate. The pyrophosphate group is in the a-configuration, is quite labile, and almost certainly reacts enzymaticaUy as the magnesium complex. It has been chemically synthesized by Tener and Khorana 33). 

We have said little about selective reactions of pentoses so we shall turn now to the synthesis of nucleotides such as AMP. In nature, ribose is phosphorylated on the primary alcohol to give ribose-5-phosphate. This is, of course, an enzyme-catalysed reaction but it shows straightforward chemo-selectivity such as we should expect from a chemical reaction. 

You will notice that these two reactions illustrate the flexibility with which ATP can activate biological molecules. In the first reaction, the nucleophilic OH group of ribose attacks the terminal phosphate group, but in the second the OH group must attackthe middle phosphate residue. This would be impossible to control chemically. 

Nucleoside Cyclic Phosphates. - Two novel fluorescent analogues of the secondary messenger molecule cyclic ADP-ribose (cADPR) have been pre-pared. Reaction of e-NAD (73) with sodium bromide in DMF in the presence of triethylamine gave the 9-cyclic ADP-ribose 74 whilst the enzyme catalysed cyclisation using Aplysia californica gives the N1-alkylated (equivalent to N7 in adenine) product. The novel cyclic etheno-CDP-ribose 75 was obtained by the enzymatic route and by the chemical cyclisation, albeit in poor yield in the latter case. A P NMR characterisation of cyclic ADP-ribose (cADPR) and its 2 -phospho-cyclic ADP-ribose has been published. ... 

Glucose-6-dehydrogenase is responsible for the first step in a chemical pathway that converts glucose (a type of sugar found in most carbohydrates) to ribose-5-phosphate. Ribose-5-phosphate is an important component of nucleotides, which are the building blocks of DNA and its chemical cousin RNA. This chemical reaction produces a molecule called NADPH, which plays a role in protecting cells from potentially harmful molecules called reactive oxygen species. These molecules are byproducts of normal cellular functions. 

I. Reactions of Hypoxanthine. The fact that hypoxanthine is an active intermediate in normal cells directs attention to the three chemical reactions hypoxanthine can undergo in the mammal (Fig. 2). It can be converted to inosine by reaction of the purine with ribose 1-phosphate catalyzed by purine nucleoside phosphorylase. This reaction is probably primarily a phosphorolytic reaction, in vivo, and converts inosine to hypoxanthine and probably does not function to convert hypoxanthine to inosine. There does exist a limited concentration of... 

A rapid, high yield synthesis of C-enriched intermediates of the pentose-phosphate pathway has been developed based on a combination of chemical and enzymic reactions. [l- C]Ribose and [l- C]arbinose 5-phospha,tes, available by the classical Kiliani method, were converted to a variety of specifically labelled 5-, 6-, 7-, and 8-carbon sugar phosphates (e.g.. D-erythro-pentulosc 5-phosphate, sedoheptulose mono- and di-phosphates) with the help of aldolase, transaldolase, and transketolase. ... 

---