Xanthine, xanthosine and its nucleotides: solution structures of neutral and ionic forms, and relevance to substrate properties in various enzyme systems and metabolic pathways.

• Authors: Ewa Kulikowska , Borys Kierdaszuk , David Shugar
• Languages of publication: EN

Abstracts

EN

The 6-oxopurine xanthine (Xan, neutral form 2,6-diketopurine) differs from the corresponding 6-oxopurines guanine (Gua) and hypoxanthine (Hyp) in that, at physiological pH, it consists of a ≈ 1:1 equilibrium mixture of the neutral and monoanionic forms, the latter due to ionization of N(3)-H, in striking contrast to dissociation of the N(1)-H in both Gua and Hyp at higher pH. In xanthosine (Xao) and its nucleotides the xanthine ring is predominantly, or exclusively, a similar monoanion at physiological pH. The foregoing has, somewhat surprisingly, been widely overlooked in studies on the properties of these compounds in various enzyme systems and metabolic pathways, including, amongst others, xanthine oxidase, purine phosphoribosyltransferases, IMP dehydrogenases, purine nucleoside phosphorylases, nucleoside hydrolases, the enzymes involved in the biosynthesis of caffeine, the development of xanthine nucleotide-directed G proteins, the pharmacological properties of alkylxanthines. We here review the acid/base properties of xanthine, its nucleosides and nucleotides, their N-alkyl derivatives and other analogues, and their relevance to studies on the foregoing. Included also is a survey of the pH-dependent helical forms of polyxanthylic acid, poly(X), its ability to form helical complexes with a broad range of other synthetic homopolynucleotides, the base pairing properties of xanthine in synthetic oligonucleotides, and in damaged DNA, as well as enzymes involved in circumventing the existence of xanthine in natural DNA.

Keywords

EN

enzyme reactions; prototropic tautomerism; xanthine; caffeine biosynthesis; metabolic pathways; G proteins; base pairing; xanthosine; acid/base properties; nucleotides

• Publisher: Polish Biochemical Society
• Journal: Acta Biochimica Polonica
• Year: 2004
• Volume: 51
• Issue: 2
• Pages: 493-531

Dates

published

2004

received

2004-05-09

Contributors

author

Ewa Kulikowska

• Department of Biophysics, Institute of Experimental Physics, University of Warsaw, 93 Zwirki i Wigury, 02-089 Warszawa, Poland

author

Borys Kierdaszuk

• Department of Biophysics, Institute of Experimental Physics, University of Warsaw, 93 Zwirki i Wigury, 02-089 Warszawa, Poland

author

David Shugar

• Department of Biophysics, Institute of Experimental Physics, University of Warsaw, 93 Zwirki i Wigury, 02-089 Warszawa, Poland

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