Structure of L-Arginyl-L-aspartie Acid Dihydrate

C~0H~gN5Os.2H20, Mr=325.32, monoclinic,P2~, a = 12.029 (2), b=4.904 (2), c=13.215 (2) A, fl= 107.68 (2) ° , F= 743 (1) A 3, Z= 2,D m = 1-45, D x = 1.45 Mg m -3, Cu Ka, 2 = 1.54184 A,fl= 1.01mm -1, F(000)=348, T=293K. The final R value for 1277 observed reflections 110 >_ 3tr(Io)l is 0.031. The dipeptide exists as a zwitterion. The arginyl side-chain conformation is similar to that found in arginyl-glutamic acid [Pandit, Seshadri & Viswamitra (1983). Acta Cryst. C39, 1669-16721. The guanidyl group forms a pair of hydrogen bonds with oxygen atoms of the backbone carboxyl group. The crystal structure is also stabilized by -bonding interactions involving both water molecules.

Effect of isonicotinic acid hydrazide-copper complex on Rous sarcoma virus and its genome RNA

The copper complex of the antituberculous drug, isonicotinic acid hydrazide (INH), inhibits the RNA-dependent DNA polymerase of Rous sarcoma virus and inactivates its ability to malignantly transform chick embryo cells. The INH-copper complex binds to the 70S genome RNA of Rous sarcoma virus (RSV), which may account for its ability to inhibit the RNA-dependent DNA polymerase. The complex binds RNA more effectively than DNA in contrast to M-IBT-copper complexes, which bind both types of nucleic acids equally. The homopolymers, poly rA and poly rU, are bound by the INH-copper complex to a greater extent than poly rC. Isonicotinic acid hydrazide alone and CuSO4 alone bind neither DNA, RNA, poly (rA), poly (rU), nor poly (rC). However, CuSO4 alone binds poly (rI); INH alone does not. In addition to viral DNA synthesis, chick-embryo cell DNA synthesis is inhibited by the INH-copper complex. The extent of inhibition of cellular DNA synthesis is greater than that of cellular RNA and protein synthesis. No selective inhibition of transformation in cells previously infected with Rous sarcoma virus is observed.

Interaction of metal ions with nucleic acids and related compounds. II. Studies on Au(III)-nucleic acid system

The nature of interaction of Au(III) with nucleic acids was studied by using methods such as uv and ir spectrophotometry, viscometry, pH titrations, and melting-temperature measurements. Au(III) is found to interact slowly with nucleic acids over a period of several hours. The uv spectra of native calf-thymus DNA 9pH 5.6 acetate buffer containing (0.01M NaCIO4) showed a shift in λ max to high wavelengths and an increase in optical density at 260 nm. There was a fourfold decrease in viscosity (expressed as ηsp/c). The reaction was faster at pH 4.0 and also with denatured DNA (pH 5.6) and whole yeast RNA (pH 5.6). The order of preference of Au(III) (as deduced from the time of completion of reaction) for the nucleic acids in RNA > denatured DNA > DNA. The reaction was found to be completely reversible with respect KCN. Infrared spectra of DNA-Au(III) complexes showed binding to both the phosphate and bases of DNA. The same conclusions were also arrived at by melting-temperature studies of Au(III)-DNA system. pH titrations showed liberation of two hydroxylions at r = 0.12 [r = moles of HAuCl4 added per mole of DNA-(P)] and one hydrogen ion at r = 0.5. The probable binding sites could be N(1)/N(7) of adenine, N(7) and/or C(6)O of guanine, N(3) of cytosine and N(3) of thymine. DNAs differing in their (G = C)-contents [Clostridium perfingens DNA(G = C, 29%), salmon sperm DNA (G + C, 42%) and Micrococcus lysodeikticus DNA(G + C, 29%), salmon sperm DNA (G = C, 72%)] behaved differently toward Au(III). The hyperchromicity observed for DNAs differing in (G + C)-content and cyanide reversal titrations indicate selectivity toward ( A + T)-rich DNA at lw values of r. Chemical analysis and job's continuous variation studies indicated the existence of possible complexes above and below r = 1. The results indicate that Au(III) ions probably bind to hte phosphate group in the initial stages of the reaction, particularly at low values of r, and participation of the base interaction also increases. Cross-linking of the two strands by Au(III) may take place, but a complete collapse of the doulbe helix is not envisaged. It is probable that tilting of the bases or rotaiton of the bases around the glucosidic bond, resulting in a significant distrotion of the double helix, might take place due to binding of Au(III) to DNA.