Nucleotides such as Adenosine

Some glycosyl transferases show an unusual double substrate specificity that is, they strongly favor as substrates a pair of unrelated sugar nucleotides, such as adenosine and uridine derivatives.505... 

The major problem in the identification of P2Y receptor-mediated inhibition of ATP on neurotransmitter release lay in the difficulty to clearly exclude breakdown to adenosine and an involvement at Ai receptors. However, the demonstration that ATP acted per se on P2 receptors obtained a solid support when it was shown that breakdown-resistant nucleotides such as adenosine 5 -[y-thio]triphosphate (ATPyS) and py-methyleneadenosine-5 -triphosphate (p,y-MeATP) mimicked the effects of... 

In addition to the usual adenine nucleotides (such as adenosine 5-phosphate, adenosine 5-pyrophosphate, and adenosine 5-triphosphoric acid) present in bacterial extracts, several adenine nucleotides of uncertain structure have been reported. These substances, termed adenylyl peptides have been isolated from trichloroacetic acid extracts of Staphylococcus aureus ... 

Urease catalyzes the hydrolysis of urea to ammonia, while catalase is capable of rapidly decomposing II2O2 to H2O + 02. " In a number of cases, enzyme catalysis requires the participation of a smaller molecule usually referred to as a coenzyme. Many of the vitamins and simple nucleotides such as adenosine triphosphate (ATP) have been shown to act as coenzymes. 

Dietary purines are largely catabolized in the gut, rather than used by the body for the synthesis of nucleic acids. The end-product of purine catabolism in humans is uric add. The diet accounts f[ir less than half of the uric add appearing in the bloodstream, Most of the plasma uric add, or urate, originates from catabolism of the purines synthesized by the body (endogenous purines). The major purines are adenine and guanine. They occur mainly as nucleotides, such as adenosine triphosphate (ATP) and guanosine triphosphate (GTP), and as parts of nucleic acids. For example, the adenine in (UvfA occurs as adenosine monophosphate, and the adenine in DNA occurs as deoxyadenosine monophosphate. 

A nucleoside consists of a purine or pyrimidine base linked to a pentose, either D-ribose to form a ribonucleo-side or 2-deoxy-D-ribose to form a deoxyribonucleoside. Three major purine bases and their corresponding ribo-nucleosides are adenine/adenosine, guanine/guanosine and hypoxanthine/inosine. The three major pyrimidines and their corresponding ribonucleosides are cytosine/ cytodine, uracil/uradine and thymine/thymidine. A nucleotide such as ATP (Fig. 17-1) is a phosphate or polyphosphate ester of a nucleoside. 

The purine and pyrimidine ring compounds found in nucleic acids are known as "bases," even though some of them have almost no basic character. Nucleosides are the N-glycosyl derivatives of the bases with ribose or 2-deoxyribose. Tire nucleotides are phosphate esters of nucleosides. Similar names are applied to related compounds such as adenosine triphosphate (ATP) that are not present in DNA or RNA. The names of the principal nucleotides from which the nucleic acids are formed are given in Table 5-1. The... 

ADENINE. [CAS 73-24-5]. A prominent member of the family of naturally occurring purines (see Structure 1). Adenine occurs not only in ribonucleic adds (RNA), and deoxyribonucleic acids (DNA). but in nucleosides, such as adenosine, and nucleotides, such as adenylic acid, which may be linked with enzymatic functions quite apart from nucleic adds. Adenine, in the form of its ribonucleotide, is produced in mammals and fowls endogenously from smaller molecules and no nutritional essentiality is ascribed to it. In the nucleosides, nucleotides, and nucleic acids, the attachment or the sugar moiety is at position 9. 

Abstract Adenine-based purines, such as adenosine and ATP, are ubiquitous molecules that, in addition to their roles in metabolism, act as modulators of neurotransmitter release through activation of presynaptic PI purinoceptors or adenosine receptors (activated by adenosine) and P2 receptors (activated by nucleotides). Of the latter, the P2Y receptors are G protein-coupled, whereas the P2X receptors are ligand-gated ion channels and not covered in this review. 

While the PRTases salvage nucleobases within cells, nucleosides such as adenosine and uridine are present in the blood at much higher concentrations ( 1 pM) than the equivalent nucleobases, adenine and uracil. Indeed, the brain synthesizes pyrimidine nucleotides (UTP and CTP) via salvage synthesis from uridine produced by the liver and released into the circulation. Human cells may contain at least three types of nonspecific nucleoside transporters, and nucleosides are internalized more rapidly than nucleobases. 

A liquid ion evaporation MS - MS study has been reported for nucleotides that usually do not produce intense molecular ions. It was suggested that this technique might be superior to f PD, Cl-MS, DCI, FAB, secondary ion mass spectrometry (SIMS), and ion thermospray for some compounds of great biochemical importance such as adenosine triphosphate (ATP). 

Subtypes of adenosine receptors exist - A, Aj and A3 -which have differential sensitivities to adenosine nucleoside analogues, including 2-methylthio-AMP, 2-thioadenosine, DPMA. IB-MECA, NECA, CPA. CCPA and DPCPX. These receptors, and subtypes within A2, have all been cloned. They have structures typical of the seven-transmembrane G-protein-coupled superfamily of receptors, but have amongst the shortest sequences known (A3 has only 318 amino acids), and a lack of sequence similarity with any other receptors appears to put them in a class of their own. Adenosine receptors are not sensitive to nucleotides such as ADP (adenosine diphosphate) and ATP (adenosine triphosphate), which instead act as P2 receptor agonists that are nucleotide-... 

Compounds that serve as energy carriers for the chemotrophs, linking catabolic and biosynthetic phases of metabolism, are adenosine phosphate and reduced pyridine nucleotides (such as nicotinamide dinucleotide or NAD). The structure of adenosine triphosphate (ATP) is shown in Fig. 1. It contains two energy-rich bonds, which upon hydrolysis, yield nearly eight kcal/mole for each bond broken. ATP is thus reduced to the diphosphate (ADP) or the monophosphate (AMP) form. 

Nucleotides are generally defined as phosphoric esters (of the carbohydrate moiety) of nucleosides. In polymerized forms (involving phospho-diester linkages), the nucleotides constitute the nucleic acids, which are fundamental components of all cells and viruses. Nucleotides also occur as mixed anhydrides, such as adenosine 5 -triphosphate and uridine 5 -(q -d-glucopyranosyl pyrophosphate), which comprise an important class of... 

Polymer-supported macrocycles A and B are able to take up nucleotide phosphates such as adenosine di- and triphosphate (ADP and ATP) at pH 4... 

If nucleosides such as adenosine are esterified with phosphoric acid they form nucleotides, e.g. adenosine monophosphate (AMP) ... 

Each nucleoside can react with phosphoric acid or a phosphoric acid derivative to form a phosphate ester (see Chapter 20, Section 20.12). The phosphate ester of a nucleoside is called a nucleotide. Using adenosine (113) as an example, there are three possible monophosphate esters 126, 127, and 128. These compounds are named adenosine 5 -monophosphate, adenosine 3 -monophosphate, and adenosine 2 -monophosphate. It is also possible to attach a second phosphate unit to the first to make a diphosphate such as adenosine 5 -diphosphate (129), and three phosphate units may be attached as in adenosine 5 -triphosphate (130). 

Cyclic nucleotides such as cyclic adenosine 3, 5 -monophosphate (cAMP) and cyclic guanosine 3, 5 -mono-phosphate (cGMP) play an important role in cellular signalling as second messengers in response to, for instance, neurotransmitters or hormones. The initial action involves the (hormone) interacting with a G protein-coupled... 

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