Adenine characteristics

Another property of pyrimidines and purines is their strong absorbance of ultraviolet (UV) light, which is also a consequence of the aromaticity of their heterocyclic ring structures. Figure 11.8 shows characteristic absorption spectra of several of the common bases of nucleic acids—adenine, uracil, cytosine, and guanine—in their nucleotide forms AMP, UMP, CMP, and GMP (see Section 11.4). This property is particularly useful in quantitative and qualitative analysis of nucleotides and nucleic acids. 

Price, R., Gaber, B. and Lvov, Y. (2001) In-vitro release characteristics of tetracycline, khellin and nicotinamide adenine dinudeotide from halloysite a cylindrical mineral for delivery of biologically active agents. Journal of Microencapsulation, 18, 713—723. 

Treatment of 9-(/ -D-ribofuranosyluronic acid)adenine with diphenylphosphoro-chloridate and orthophosphate or tripolyphosphate yields (62) and (63), which, although unstable, inhibit rabbit AMP aminohydrolase and pyruvate kinase, respectively, with behaviour characteristic of active-site-specific reagents.98 Adenylate kinases from several sources are inactivated by iV6-[2- and 4-fluorobenzoyl]-adenosine-5 -triphosphates, with kinetics characteristic of active-site labelling, although these compounds were without effect on yeast hexokinase and rabbit pyruvate kinase.99... 

Figure 2. Characteristics of adenine nucleotide exchange that define actin polymerization and depolymerization zones within cells.

The derivative (9) of 3,6-dideoxy-a-D-xyIo-hexopyranose (abequose) was isolated from a strain of Salmonella typhimurium,16 that (10) of 3,6-dideoxy-a-D-nfco-hexopyranose (paratose) from Salmonella paratyphi,54 and a mixture of 10 and the ester (11) of 3,6-dideoxy-a-D-arabino-hexopyranose (tyvelose) from Salmonella enteritidis.,6 It was shown that these derivatives are formed from cytidine 5 -(a-D-glu-copyranosyl pyrophosphate) by treatment with nicotinamide adenine dinucleotide (NAD+) and reduced nicotinamide adenine dinucleotide phosphate (NADPH) in the presence of cell extracts of the respective bacterial strain. For example, formation of 9 is characteristic of preparations from Salmonella, group B,55,56 or Pasteurella pseudotuberculosis, type II.56 The derivative 10 was obtained with extracts of Salmonella, group A,56 and Pasteurella pseudotuberculosis, type I and III,56 and a mixture of 10 and 11 with those of Salmonella, group D,55-60 or Pasteurella pseudotuberculosis, type IV 56.59,60 Under similar conditions, the ester (12) of cytidine 5 -pyro-... 

A complete understanding of the biochemical functions of DNA requires a clear picture of its structural and physical characteristics. DNA has significant absorption in the UV range because of the presence of the aromatic bases adenine, guanine, cytosine, and thymine. This provides a useful probe into DNA structure because structural changes such as helix unwinding affect the extent of absorption. In addition, absorption measurements are used as an indication of DNA purity. The major absorption band for purified DNA peaks at about 260 nm. Protein material, the primary contaminant in DNA, has a peak absorption at 280 nm. The ratio A26(j/A2m is often used as a relative measure of the nucleic acid/protein content of a DNA sample. The typical A260/Am for isolated DNA is about 1.8. A smaller ratio indicates increased contamination by protein. 

All nucleic acids consist of covalently linked nucleotides. Each nucleotide has three characteristic components (1) a purine or pyrimidine base (2) a pentose and (3) a phosphate group. The purine or pyrimidine bases are linked to the C-T carbon of a deoxyribose sugar in DNA or a ribose sugar in RNA. The phosphate groups are linked to the sugar at the C-5 and C-3 positions. The purine bases in both DNA and RNA are always adenine (A) and guanine (G). The pyrimidine bases in DNA are thymine (T) and cyto-... 

Another characteristic of enzymes is their frequent need for cofactors. A cofactor is a nonprotein compound that combines with the otherwise inactive enzyme to give the active enzyme. Examples of cofactors are metal ions such as Ca2+, Cu2+, Co2+, Fe2+, and Mg2+, and organic molecules such as nicotinamide adenine dinucleotide (NAD) and flavin adenine dinudeotide (FAD). 

Tissue also contains some endogenous species that exhibit fluorescence, such as aromatic amino acids present in proteins (phenylalanine, tyrosine, and tryptophan), pyridine nucleotide enzyme cofactors (e.g., oxidized nicotinamide adenine dinucleotide, NADH pyridoxal phosphate flavin adenine dinucleotide, FAD), and cross-links between the collagen and the elastin in extracellular matrix.100 These typically possess excitation maxima in the ultraviolet, short natural lifetimes, and low quantum yields (see Table 10.1 for examples), but their characteristics strongly depend on whether they are bound to proteins. Excitation of these molecules would elicit background emission that would contaminate the emission due to implanted sensors, resulting in baseline offsets or even major spectral shifts in extreme cases therefore, it is necessary to carefully select fluorophores for implants. It is also noteworthy that the lifetimes are fairly short, such that use of longer lifetime emitters in sensors would allow lifetime-resolved measurements to extract sensor emission from overriding tissue fluorescence. 

The effect of metal coordination to any of the endocyclic N atoms can be also expressed in terms of a loss in basicity of the remaining endocyclic N atoms, hence in a reduced tendency to accept a proton and to become a metalated adeninium cation. As the pXa values of these species are frequently in the range 2-0, their determination usually is facile. In the case of Ptn binding to 9-MeA, relevant pXa values are 1.93 0.1 for N7 coordination and 0.45 0.11 for N1 coordination in the mixed nucleobase complex di-[(NH3)2Pt(9-MeA)(l-MeC-A5)]2+ (103). This characteristic difference permits a ready assignment of the metal binding site in Pt(II) adenine complexes. The apparent increase in basicity of N7 upon N1 Pt(II) binding disappears if microacidity constants are applied (103). 

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