Calorimetric investigation of the helix-coil conversion of polyuridylic acid

The heats of the conformational conversion ΔH_c of polyuridylic acid (polyU) in the presence of various cations were determined using a differential scanning microcalorimeter and an isothermal mixing calorimeter. The first method yields a value of ΔH_c = 5.2 kcal/mol of base pairs, the second one a value of ΔH_c = 6.4 kcal/mol of base pairs. Knowing ΔH_c and the maximal slope of the degree of conversion, which was determined from the temperature dependence of the absorbance of polyU solutions at 260 nm, we were able to evaluate the parameter of cooperativity σ. From the relation σ = e the stacking free energy ΔF_stack could be calculated. Dividing the apparent enthalpy of conversion by the calorimetrically measured enthalpy yields the cooperative length N₀ of one helical segment at the midpoint of conversion. The results show that the type of the cation has no influence on the magnitude of ΔH_c, whereas the cooperativity of polyU is influenced by the various cations.     

Polysaccharide-polynucleotide complexes VIII. Cation-induced complex formation between polyuridylic acid and schizophyllan

Raman spectroscopy has recently been applied ex vivo and in vivo to address various biomedical issues such as the early detection of cancers, monitoring of the effect of various agents on the skin, determination of atherosclerotic plaque composition, and rapid identification of pathogenic microorganisms. This leap in the number of applications and the number of groups active in this field has been facilitated by several technological advancements in lasers, CCD detectors, and fiber-optic probes. However, most of the studies are still at the proof of concept stage. We present a discussion on the status of the field today, as well as the problems and issues that still need to be resolved to bring this technology to hospital settings (i.e., the medical laboratory, surgical suites, or clinics). Taken from the viewpoint of clinicians and medical analysts, the potential of Raman spectroscopic techniques as new tools for biomedical applications is discussed and a path is proposed for the clinical implementation of these techniques.     

Oligonucleotide interactions. I. Structure of 2:1 complexes between polyuridylic acid and oligoadenylic acid

The circular dichroism of a number of 1:2 complexes between oligoadenylic acid and polyuridylic acid has been measured. The structure of these complexes, as evidenced by their optical properties, is independent of the chain length of the oligonucleotide throughout all ranges of chain lengths from adenosine to high molecular weight polyadenylic acid. A similar structure was found for the complex (Ap)₅A:2(Up)₅U.     

Complex formation between spin-labeled polyuridylic acid and pyrimidine nucleosides.

Complex formation between poly (U) and pyrimidine nucleosides, uridine and cytidine, was observed using spin labeling technique. The binding of these nucleosides with poly (U) takes place within a narrow range of their concentration and is characterized by a relatively strong cooperativity. It is shown, that both hydrogen bonding and stacking interaction contribute to the complex stability. Some thermodynamic parameters of the process were obtained from the binding isotherms. At 21 degrees C the equilibrium constants for nucleation were found to be 0.23 M-1 and 0.42 M-1, and those for chain growth 2.63 M-1 and 2.19 M-1 for uridine and cytidine respectively. Complex formation of poly (U) with adenosine was also studied by spin labeling method.     

Interaction between polyuridylic acid and rabbit globin messenger ribonucleic acid

Poly(U) binds to globin mRNA in 0.1m-NaCl. Studies with ribonuclease digestion of this complex suggest that there are polyadenylate-rich sequences in the mRNA containing about 30-40 adenylate residues. The sequences appear to be homogenous and of approximately the same length for both alpha- and beta-globin mRNA. They are most likely located at the 3' terminus of the molecule.     

Exchange of adenylic nucleotides and bacterial growth]

Adenylic nucleotides pool reaches optimum with biomass. The ATP quantity decreases after exponential growth. AMP increases when ATP decreases. Energetic load is optimum two hours before optimum growth. E. coli prevent the growth of Pseudomonas. AMP is discharged in the medium at the beginning of growth of E. coli and every time by Pseudomonas.     

Complex formation between polyuridylic acid and adenosine using spin-labeling

2 poly(u) . 1 adenosine complex formation was studied by spin-technique in the temperature range from 7 to 25 degrees C. It is shown that adenosine binding induces the conformational transition of poly(u) structure from flexible coil into rigid helix. The contribution of hydrogen bonding and stacking of adenosine to the total change of enthalpy and entropy upon complex formation was estimated.     

Proton magnetic resonance study of complex formation between N6-methyladenosine and polyuridylic acid

The interaction between N₆-methyladenosine and polyuridylic acid in D₂O solution at neutral pD has been studied as a function of temperature and N₆-methyladenosine concentration by proton magnetic resonance spectroscopy. A rigid double-stranded 1:1 complex is formed below ～10°C, involving hydrogen-bonded N₆-methyladenine:uracil base-pairing and stacking of the adenine bases. This complex is less stable than the 1:2 complex formed between adenosine and polyU, and involves a more rapid exchange of the monomer between free and polymer-bound environments.     

Thermodynamic study of the formation of adenine nucleotide-manganese complexes. II. Calorimetric results.

Enthalpic variations in the formation of adenine nucleotide-manganese complexes, as measured by microcalorimetry, are reported. All the results are obtained in the temperature range 6--30 degrees C at I =0.2 and pH values 7.00 or 7.50. All the reactions are endothermic and the deltaH values increase with the length of the phosphate chain and with temperature. The deltaH values are compared with those previously obtained for adenine nucleotide-manganesium complexes. The comparison between calorimetric and potentiometric deltaH values is made. The divergence observed between these results at low temperature leads us to assume the formation of nucleotide aggregates induced by the presence of manganese ions. This hypothesis is confirmed by differential ultraviolet spectra.     

Platinum complexes of nucleotides.

The reaction of [Pt(dien)Cl1Cl (dien = NH2CH2CH2NHCH2CH2NH2) with nucleotides has been studied by nuclear magnetic resonance. It has been found that the CMP (cytidine 5'-monophosp-ate) and GMP (guanosine 5'-monophosphate/coordinate to the platinum atom through N3 and N7, respectively. The reaction of the platinum salt with the nucleotide is complete when one to one ratio of platinum to nucleotide is used and no evidence of phosphate group binding to platinum has been found. No additional binding sites have been detected except the N7 site on the guanylic group of GMP even in the presence of a large excess of [Pt(dien) Cl1Cl. The AMP (adenosine 5'monophosphate] coordinates to the platinum at the N1 and/or N7 sites. The reaction of AMP and platinum is complete is complete at a ratio of four platinum to one AMP.     

Polyadenylic.polyuridylic acid in the cotreatment of cancer

The biological properties of polyadenylic . polyuridylic acid (Poly(A) . Poly(U] are discussed and the application to the treatment of cancer in various animal models is described. Pharmacokinetic properties are presented and the results of clinical application to humans with specific reference to adjuvant treatment of breast cancer are examined in some detail. Given these results and the total lack of toxicity or of secondary effects of Poly(A) . Poly(U) it appears that further development and application of this polynucleotide complex are certainly justified in terms of clinical use in cancer and perhaps in viral pathologies.