PubMed Health⌕ Search

Biomedical subjects

M A Viswamitra

Publications and source records attributed to M A Viswamitra.

33 records · Page 2Linked to original sources
PubMed1981

Crystalline A-dna: the X-ray analysis of the fragment d(G-G-T-A-T-A-C-C).

An A-DNA type double helical conformation was observed in the single crystal X-ray structure of the octamer d(G-G-T-A-T-A-C-C), 1, and its 5-bromouracil-containing analogue, 2. The structure of the isomorphous crystals (space group P61) was solved by a search technique based on packing criteria and R-factor calculations, with use of only low order data. At the present stage of refinement the R factors are 31% for 1 and 28% for 2 at a resolution of 2.25 A (0.225 nm). The molecules interact through their minor grooves by hydrogen bonding and base to sugar van der Waals contacts. The stable A conformation observed in the crystal may have some structural relevance to promoter regions where the T-A-T-A sequence is frequently found.

Base Sequence↗
PubMed1980

Interactions of tris buffer with nucleotides: the crystal structure of tris(hydroxymethyl)methylammonium adenosine 5'-diphosphate dihydrate.

The crystal and molecular structures of the Tris salt of adenosine 5'-diphosphate were determined from X-ray diffraction data. The crystals are monoclinic, space P21, and Z = 2 with a=9.198 (2) A, b=6.894 (1) A, c=18.440 (4) A, and beta = 92.55 (2) degrees. Intensity data were collected on an automated diffractometer. The structure was solved by the heavy-atom technique and refined by least squares to R = 0.047. The ADP molecule adopts a folded conformation. The conformation about the glycosidic bond is anti. The conformation of the ribose ring is close to a perfect C(2')-endo-C-(3')-exo puckering. The conformation about C(4')-C(5') is gauche-gauche, similar to other nucleotide structures. The pyrophosphate chain displays a nearly eclipsed geometry when viewed down the P-P vector, unlike the staggered conformation observed in crystal structures of other pyrophosphates. The less favorable eclipsed conformation probably results from the observed association of Tris molecules with the polar diphosphate chain through electrostatic interactions and hydrogen bonds. Such interactions may play an important role in Tris-buffered aqueous solutions of nucleotides and metal ions.

Adenosine Diphosphate↗
PubMed1975

Molecular structures of cytidine-5'-diphosphate and cytidine-5'-diphospho-choline, and their role in intermidiary metabolism.

The nucleotide coenzyme cytidine-5'-diphospho-choline is highly folded. The CMP-5' parts of the molecules in the crystal structure are strongly linked by metal ligation and hydrogen bonds leaving the phosphoryl-choline residues relatively free. Cytidine-5'-diphosphoric acid exists as a zwitterion with N31 protonated. The P-O bond lengths from the anhydride bridging oxygen in the pyrophosphate are significantly different.

Choline↗
PubMed1973

Cytidylic acid "a" trihydrate: structure and conformation.

Cytidylic acid "a" (cytidine 2'-monophosphate) crystallizes in the triclinic space group P1 with two molecules of cytidine monophosphate (C(9)H(14)O(8)N(3)P) and six molecules of water in the unit cell. X-ray analysis of this crystal shows that in both molecules, the base is in the anti conformation, the ribose ring is C(2')-endo puckered, and the hydroxyl O(5') is gauche-gauche. The two molecules are linked by a short hydrogen bond through the phosphate oxygens.

Cytosine Nucleotides↗
PubMedDate not supplied

Interaction of Co, Mn, Mg and Al with d(GCGTACGC): a spectroscopic study.

Spectroscopic study on the interactions of trace elements Co., Mn, Mg and Al with d(GCGTACGC) indicated the following: Al and Mg did not alter Tm values. Mn enhanced Tm at lower concentration and decreased it at higher concentrations. Interestingly Co at higher concentration elevated the Tm. These studies also showed lower concentrations of Mn displaced EtBr, whereas Al could displace it at higher ionic strength. Mg and Co displaced EtBr fluorescence at moderate concentrations. The binding constant values and CD spectra clearly indicated strong binding of these elements to DNA.

Aluminum↗