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

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 approximately 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.

The electrophoretical activity of the buccal epithelium cells nuclei in newborns of smoking mothers.

The electrophoretical activity of nuclei (EMN) occurs in all cells of the human body. The EMN is variable and depends on the particular stage of human ontogenesis. The factors that modify the ontogenesis may influence the electrophoretical activity of nuclei. The aim of the study was to compare the index of electrophoretical activity of nuclei (index EMN) derived from the buccal epithelium of 40-week newborns (n = 26) from healthy, single pregnancies of smoking mothers with newborns (n = 31) of non-smoking mothers. The cells of the buccal epithelium were analysed using light microscope in the environment of alternating field (voltage 20-30 V; intensity 0.1 mA; frequency 1-2 Hz) generated by Biotest processor. In each group we estimated the number of cells with mobile nuclei and cells with motionless nuclei per 100 cells being observed. The result of this research was that there is not activity of nuclei in the group of newborns of smoking mothers (index EMN = 0 with p < 0.05). The absence of activity of nuclei makes it impossible to use the EMN method for estimation of biological age in the group of newborns of smoking mothers.