Hypoxanthine, Adenine, Guanine

Two phosphoribosyl transferases then convert adenine to AMP and hypoxanthine and guanine to IMP or GMP (Figure 34-4). A second salvage mechanism involves phosphoryl transfer from ATP to a purine ri-bonucleoside (PuR) ... 

Other xanthines present in trace amounts in green coffee are xanthine, hypoxanthine, adenine, and guanine these are all absent from roasted coffee.3... 

The hydrolysis leads to 4-aminoimidazole-5-carboxamide, which under certain conditions can react with various partners (e.g., HCN, dicyan or formamidine) to give purines (i.e., adenine, guanine, hypoxanthine and diaminopurine). 

PES has been applied to study biologically active molecules with amino groups and their constituents like nucleic bases and related compounds (e.g. adenine, guanine, thymine, cytosine, hypoxanthine and their methyl derivatives)113-120 and amino acids92,121,122 or their methyl esters123. 

Our laboratory conducted the most extensive investigation of the 2,4,1-benzodiazaborines reported to date. We focused attention on l-hydroxy-lff-2,4,l-benzoxazaborine (50a), 1,2-dihydro-l-hydroxy-2,4,l-benzodiazaborine (50b), and 3-amino-l,2-dihydro-l-hydroxy-2,4,l-benzodiazaborine (50c) because their peripheries so closely matched the pyrimidine ring ones of the naturally occurring purines adenine, hypoxanthine, and guanine, respectively <94JA7597>. 

Deamination of aminopurines Adenine undergoes deamination to produce hypoxanthine, and guanine is deaminated to xanthine. 

As indicated in Fig. 25-18, free adenine released from catabolism of nucleic acids can be deaminated hydrolytically to hypoxanthine, and guanine can be deaminated to xanthine.328 The molybdenum-containing xanthine oxidase (Chapter 16) oxidizes hypoxanthine to xanthine and the latter on to uric acid. Some Clostridia convert purine or hypoxanthine to xanthine by the action of a selenium-containing purine hydroxylase.3283 Another reaction of xanthine occurring in some plants is conversion to the trimethylated derivative caffeine. 328b One of the physiological effects of caffeine in animals is inhibition of pyrimidine synthesis.329 However, the effect most sought by coffee drinkers may be an increase in blood pressure caused by occupancy of adenosine receptors by caffeine.330... 

Gosch and Montag (249) determined and compared the concentration of purines and pyrimidines in different coffees. The freeze-dried extract was dissolved in water, hydrolized with TFA/formic acid at 235°C, and applied to an RP18 SPE cartridge. The eluted sample (with methanol) was analyzed by HPLC on a LiChrosphere 100 RP-18. The mobile phase was a phosphate buffer containing A,A-dimethyloctylamine, and the detection was spectrophotometric at 269 nm. Adenine, guanine, hypoxanthine, xanthine, AMP, GMP, IMP, UMP, and uric acid levels were tabulated for arabica and robusta coffees from various sources. 

One enzyme uses either guanine or hypoxanthine (adenine with the amino group replaced by an OH). A second enzyme uses free adenine. A third enzyme is specific for uracil and thymine. All the enzymes carry out the same reaction transfer of the free base to the ribose-5 -monophosphate of PRPP, forming a nucleoside-5 monophosphate (NMP). 

Thymine Uracil 5-Bromouracil 5-Aminouracil (Adenine) (Hypoxanthine) (6-Methyluracil ) (Purine ) Thymine Uracil 5-Bromouracil 5-Aminouracil 5-Bromouracil Adenine Guanine Hypoxanthine 6-Methyluracil Uracil Adenine Hypoxanthine Purine (Adenine)... 

Some chemical fragments of DNA and RNA can also be found in meteorites (Tables 5.1 and 5.2). For example, some meteorites have been reported to contain small amounts of adenine, one of the nucleobases found in RNA and DNA. The current view is that the Murchison meteorite contained adenine, guanine, their hydrolysis products hypoxanthine and xanthine, and uracil. The reported concentration of all those substances, however, is low, about 1.3 ppm. The Murchison and other meteorites may also contain ribitol and ribonic acid, the reduced and oxidized forms of ribose, respectively, but ribose itself has not been found.6... 

For the purine-purine combination hypoxanthine-adenine, there are six possible base pairs with two hydrogen bonds. Of these, only two can occur in the nucleic acids, XA12 and XA22, with XA12 representing a wobble pair which is of some biological importance in transfer RNA, and comparable to the guanine-uracil wobble illustrated in Fig. 16.14. 

A transribosylase which exchanges the hypoxanthine of inosine with adenine, guanine, xanthine, thymidine, 4,5-diaminouracil, 5-bromouracil, and 4,6-diaminouracil has been found in Escherichia coli. - ... 

This enzyme represents a principal route for the return, or salvage, of purines such as hypoxanthine, adenine, and guanine to the monophosphate level. The activity requires a metal, preferably magnesium. 

Adenine, guanine, guanylurea, and several s-triazines and ureas have been detected in HCl-extracts of Orgueil and Murchison (Hayatsu, 1964 Hayatsu et al, 1968, 1975). The first 3 were confirmed by Stoks and Schwartz (1981), but the s-triazines were not they may have formed from guanylurea in the isolation and identification procedure. Other compounds detected are xanthine, hypoxanthine, and uracil (van der Velden and Schwartz, 1977 Stoks and Schwartz, 1979). A report of 4-hydroxy-pyrimidine and several related compounds (Folsorae et al, 1973) was not confirmed (Hayatsu et al, 1975 van der Velden and Schwartz, 1977) these compounds, which... 

The naturally occurring purines fall into 4 main groups. (1) Simple substituted derivatives of purine (1) such as adenine (2) and various 6-AT-substituted derivatives. (2) Monoxo-dihydropurines such as hypoxanthine (3), guanine (4), and isoguanine (5). f3) Dioxotetra-hydropurines such as xanthine (6) and methylated derivatives including the 3,7-dimethyl derivative theobromine (7), 1,3-dimethylxanthine or theophylline f8), and 1,3,7-trimethylxanthine or caffeine (9). (4) Trioxohexahydropurines such as uric acid (10). 

Most of the free purines derived from the breakdown of DNA, RNA, and nucleotides in the diet are catabolized to xanthine and then to uric acid in the gut mucosa. The AMP and GMP biosynthesized in the body can also be bmken down to free purines, such as adenine, guanine, and hypoxanthine. These purines, in contrast to those derived frcim the diet, are largely reused for the synthesis of ATP and GTP- They are first converted back to AMP or GMP in a pathway of reutiliza-lion called the purine salvage pathway. For example, adenine phosphoribosyl-transferase (PRPP) catalyzes the conversion of adenine to AMP. Here, PRPP serves as the source of the phosphoribose group. Pyrophosphate is a product of the reaction. 

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