Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.4.2.7 (adenine phosphoribosyltransferase)
 692 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Adenine (ADE) reutilisation is an important pathway of adenylate pool regeneration. Data on the rate of this process in different types of cells, its regulation and the importance of species differences is limited. In this study we evaluated adenine incorporation rate and the effect of metabolic factors on this process in human and rat endothelium and compared it to adenine phosphoribosyltransferase (APRT) activity. Microvascular endothelial cells from human (HE) and rat (RE) hearts and a transformed human microvascular endothelial cell line (HMEC-1) were investigated. The rate of adenine incorporation into the adenine nucleotide pool under control conditions was 3.1+/-0.3, 82.8+/-11.1 and 115.1+/-11.2 pmol/min per mg protein for HE, RE and HMEC-1, respectively. In the presence of 2.5 mM ribose or elevated inorganic phosphate concentration in the medium (4.8 mM), few changes were observed in all types of cells. In the presence of both ribose and high inorganic phosphate, the rate of adenine incorporation for RE and HMEC-1 was not significantly different from control, while in HE the rate of adenine incorporation into adenine nucleotides was increased by 75%. Activities of APRT in RE and HMEC-1 were 237.7+/-23.2 and 262.0+/-30.6 pmol/min per mg protein respectively while the activity in HE was markedly lower 48.7+/-3.0 pmol/min per mg protein. In conclusion, nucleotide synthesis from adenine seems to be a slow process in human cardiac microvascular endothelium but it is fast and efficient in rat heart microvascular endothelial cells. Low APRT activity in normal human endothelial cells seems to be the most likely mechanism for this. However, adenine incorporation rate and APRT activity could be greatly enhanced in human endothelium, as demonstrated in transformed cells.
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PMID:Adenine incorporation in human and rat endothelium. 1055 67

To determine the metabolic profiles of purine nucleotides and related compounds in leaves and roots of tea (Camellia sinensis), we studied the in situ metabolic fate of 10 different (14)C-labeled precursors in segments from tea seedlings. The activities of key enzymes in tea leaf extracts were also investigated. The rates of uptake of purine precursors were greater in leaf segments than in root segments. Adenine and adenosine were taken up more rapidly than other purine bases and nucleosides. Xanthosine was slowest. Some adenosine, guanosine and inosine was converted to nucleotides by adenosine kinase and inosine/guanosine kinase, but these compounds were easily hydrolyzed, and adenine, guanine and hypoxanthine were generated. These purine bases were salvaged by adenine phosphoribosyltransferase and hypoxanthine/guanine phosphoribosyltransferase. Salvage activity of adenine and adenosine was high, and they were converted exclusively to nucleotides. Inosine and hypoxanthine were salvaged to a lesser extent. In situ (14)C-tracer experiments revealed that xanthosine and xanthine were not salvaged, although xanthine phosphoribosyltransferase activity was found in tea extracts. Only some deoxyadenosine and deoxyguanosine was salvaged and utilized for DNA synthesis. However, most of these deoxynucleosides were hydrolyzed to adenine and guanine and then utilized for RNA synthesis. Purine alkaloid biosynthesis in leaves is much greater than in roots. In situ experiments indicate that adenosine, adenine, guanosine, guanine and inosine are better precursors than xanthosine, which is a direct precursor of a major pathway of caffeine biosynthesis. Based on these results, possible routes of purine metabolism are discussed.
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PMID:Profiles of purine metabolism in leaves and roots of Camellia sinensis seedlings. 2107 29

Purine bases and nucleosides are produced by turnover of nucleotides and nucleic acids as well as from some cellular metabolic pathways. Adenosine released from the S-adenosyl-L-methionine cycle is linked to many methyltransferase reactions, such as the biosynthesis of caffeine and glycine betaine. Adenine is produced by the methionine cycles, which is related to other biosynthesis pathways, such those for the production of ethylene, nicotianamine and polyamines. These purine compounds are recycled for nucleotide biosynthesis by so-called "salvage pathways". However, the salvage pathways are not merely supplementary routes for nucleotide biosynthesis, but have essential functions in many plant processes. In plants, the major salvage enzymes are adenine phosphoribosyltransferase (EC 2.4.2.7) and adenosine kinase (EC 2.7.1.20). AMP produced by these enzymes is converted to ATP and utilised as an energy source as well as for nucleic acid synthesis. Hypoxanthine, guanine, inosine and guanosine are salvaged to IMP and GMP by hypoxanthine/guanine phosphoribosyltransferase (EC 2.4.2.8) and inosine/guanosine kinase (EC 2.7.1.73). In contrast to de novo purine nucleotide biosynthesis, synthesis by the salvage pathways is extremely favourable, energetically, for cells. In addition, operation of the salvage pathway reduces the intracellular levels of purine bases and nucleosides which inhibit other metabolic reactions. The purine salvage enzymes also catalyse the respective formation of cytokinin ribotides, from cytokinin bases, and cytokinin ribosides. Since cytokinin bases are the active form of cytokinin hormones, these enzymes act to maintain homeostasis of cellular cytokinin bioactivity. This article summarises current knowledge of purine salvage pathways and their possible function in plants and purine salvage activities associated with various physiological phenomena are reviewed.
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PMID:Purine salvage in plants. 2930 99


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