Modulation by S-nitrosoglutathione (a natural nitric oxide donor) of photosystem in Pisum sativum leaves, as revealed by chlorophyll fluorescence: Light-dependent aggravation of nitric oxide effects

The reported effects of nitric oxide (NO), a signaling molecule, on the photochemical components of leaves are ambiguous. We examined the changes by a natural NO donor, S-nitrosoglutathione (GSNO). The effect of GSNO on Pisum sativum leaves was studied after a 3-hour exposure in dark, moderate (ML), or high light (HL). The NO levels in GSNO-treated samples were at their maximum under HL, compared to those under ML or dark. Most of the elevated NO was decreased by 2-4-carboxyphenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO), a NO scavenger, confirming the NO increase. Treatment with GSNO caused inhibition of photosynthesis/respiration and restricted electron transport mediated by both photosystem (PS)II and PSI. However, the inhibition by NO-donor of PSII components was stronger than those of PSI. A marked increase in the PSI acceptor side limitation [Y(NA)] and a decrease in PSI donor side limitation [Y(ND)] indicated an upregulation of cyclic electron transport, possibly to balance the damage to PSII by GSNO. We suggest that NO aggravated the HL-induced inhibition of photosynthesis and dark respiration

Preprocessing technique for DMT systems with no guard interval

Includes bibliographical references (pages [82]-83)M.S. (Master of Science

Interaction of DNA with small molecules: Role of copper histidyl peptide complexes in DNA binding and hydrolytic cleavage

1003-1015Deoxyribonucleic acid is the site of storage and retrieval of genetic information through interaction with proteins and other small molecules. Hydrolysis of the phosphodiester bond of DNA is of critical importance at several stages in a cell cycle. Thus, the development of metal complexes that cleave nucleic acids hydrolytically at physiological conditions is of great interest in the field of artificial metallonucleases. Among transition metals, Cu(II) complexes have been extensively studied in promoting hydrolysis of DNA. Histidine is a biologically important ligand for Cu(II) binding in many biological systems. Since imidazole is an efficient catalyst for ester hydrolysis at neutral pH and histidine residues are often involved in neutral hydrolytic metalloenzyme active centres and have the potential to bind to DNA, an attempt is made in this review to highlight the importance of DNA binding and cleavage and the role of a few copper histidyl peptide complexes in DNA binding and hydrolytic cleavage

Synthesis and characterization of mixed ligand complexes of zinc(ll) with cytidine and amino acids^†

1097-1101Mixed ligand complexes of Zn(II) with cytidine and amino acids, -alanine, -phenylalanine and -tryptophan have been synthesized and characterized by elemental analysis, conductivity data, electronic spectra, IR, 1H NMR and 13C NMR spectra. In these complexes, the nucleoside acts as a monodentate ligand involving only N(3) in metal coordination whereas the amino acids coordinate through carboxylate oxygen and amino nitrogen. The results drawn about binding sites of these octahedral complexes are compared with the results obtained from solution studies

Synthesis, characterization and DNA binding and cleavage properties of copper(II)-tryptophan-tryptophan complex

1638-1643Reaction of copper(II) with tryptophan-tryptophan yields a 1:2 chloro bis(trp-trp) cuprate(II) complex. The complex exhibits absorption band at 620 nm (ε = 130 M -1 cm-1), which suggests a square pyramidal geometry at Cu(II) as observed for other Cu(II)-peptide complexes. The giso value of 2.09 for the complex agrees with a Cu(II) environment of distorted square pyramidal geometry. The mononuclear complex binds to calf thymus DNA through moderate intercalative and weak covalent interactions. It converts the supercoiled plasmid pUC19 DNA to the nicked circular form under physiological conditions

DNA hydrolytic cleavage by stable Zn(II) dipeptide complexes

2329-2332Interaction of zinc with dipeptides cysteinylglycine, histidylphenylalanine and histidylserine has been investigated at 35oC and 0.1M ionic strength and the stabilities of these complexes determined. The binding modes and the geometry have been established with the help of pH metry and 1H NMR and UV visible spectra. The DNA binding and cleavage abilities of these zinc dipeptide complexes have been probed. The results demonstrate the efficiency of these complexes in the DNA cleavage

A new S<SUB>4</SUB>-ligated zinc-peptide 1 : 2 complex for the hydrolytic cleavage of DNA

A new sulfur-ligated Zn-peptide 1 : 2 complex, [ZnII(Boc-NH-Cys-Gly-Cys-OMe)2]2- (2), was prepared, characterized, and tested for its DNA-binding and -cleavage properties. Complex 2 was found to cleave DNA hydrolytically. The negative charge in 2 reduces the affinity of the complex for DNA, and enhances its binding specificity

Interaction of Ni(II)-ethylenediamine/histamine with histidylglycine and investigation of their DNA cleavage abilities

761-768The interaction of Ni(II)-ethylenediamine (en)/histamine(hist) with histidylglycine(his-gly) and their DNA cleavage abilities have been investigated. The stability constants for the Ni(II)-en-his-gly (1) and Ni(II)-hist-his-gly (2) complexes have been determined at 298.0 K and 0.10 M (KNO3) ionic strength. Both the 1:1:1 ternary complexes have been corroborated by species distribution curves and ESI-MS analysis. The complex geometries have been analyzed by UV-vis experiments and molecular mechanics simulations. The DNA binding abilities of these complexes have been established by UV-vis-absorption, thermal-denaturation and fluorescence spectroscopy. The intrinsic binding constants for the bound complexes, Ni(II)-en-his-gly:DNA and Ni(II)-hist-his-gly:DNA, have been determined to be 280 and 420 M-1 respectively. Gel-electrophoresis experiments reveal that 1 and 2 cleave supercoiled DNA (type-I) to the nicked-circular (type-II) form hydrolytically at physiological pH. A tentative mechanism is proposed for the cleavage