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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)

The nucleotide sequence of a Saccharomyces cerevisiae gene encoding a potential adenine phosphoribosyltransferase (APRT) has been determined. The protein encoded by this gene shows a high degree of similarity with APRTs from a variety of other species. The S. cerevisiae gene, named APT2, has been mapped to chromosome IV. The sequence has been deposited in the GenBank data library under Accession Number L14434.
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PMID:A Saccharomyces cerevisiae gene encoding a potential adenine phosphoribosyltransferase. 794 49

The yeast Saccharomyces cerevisiae has two separate genes (APT1 and APT2) that encode two potentially different forms of adenine phosphoribosyltransferase (APRT). However, genetic analysis indicated that only APT1 could code for a complementing activity. Cloning and expression of both the APT1 and APT2 genes in Escherichia coli showed that although discrete proteins (APRT1 and APRT2) were made by these genes, only APRT1 had detectable APRT activity. Northern and Western blot analyses demonstrated that only APT1 was transcribed and translated under normal physiological conditions in yeast. Phylogenetic analysis revealed that APRT1 and APRT2 are evolutionary closely related and that they arise from a gene duplication event. We conclude that APT1 is the functional gene in S. cerevisiae and that APT2 is a pseudogene.
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PMID:APT1, but not APT2, codes for a functional adenine phosphoribosyltransferase in Saccharomyces cerevisiae. 986 50

Adenine phosphoribosyltransferase (APT; EC 2.4.2.7) is a constitutively expressed enzyme involved in the one-step salvage of adenine to AMP. The Arabidopsis thaliana genome contains five sequences annotated as encoding APT or APT-like enzymes. Three of these have now been cloned, over-expressed and compared using kinetic analyses. At a cytosolic pH, all bind adenine efficiently based on their Km values (0.8-2.6 &mgr;M), although APT1 metabolizes adenine at a rate 31-53 times faster than APT2 and APT3, respectively. Since APT also has a possible role in the interconversion of cytokinin bases to nucleotides, we characterized the activity of each isoform on zeatin, isopentenyladenine and benzyladenine. Based on their Km values, APT2 and APT3 had much higher affinities than APT1 for all three cytokinins (15-440 &mgr;M for APT2 and 3 vs. 1.8-2.5 mM for APT1); conversely the Vmax values for APT2 and APT3 on these CK substrates showed the opposite trend, being 4- to 19-fold lower than those of APT1. Anti-peptide antibodies for APT1, APT2, and APT3 were prepared and used to examine the subcellular localization of each isoform. Based on these results, APT1 and APT3 appear to be cytosolic, while the localization of APT2 was inconclusive although sequence analysis implies that APT2 is also cytosolic. Each isoform was modelled against the crystal structure of APT from Leishmania donovani, and structural differences in substrate specificity-determining domains have been found. The estimated kinetic activities of these APTs suggest that they contribute primarily to adenine recycling, although an involvement in cytokinin interconversion cannot be discounted.
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PMID:Adenine phosphoribosyltransferase isoforms of Arabidopsis and their potential contributions to adenine and cytokinin metabolism. 1201 Apr 67