Spectroscopic and molecular docking studies on interaction of two Schiff base complexes with bovine serum albumin

Abstract

This study was designed to examine interaction of two ternary copper (II) Schiff base complexes with bovine serum albumin (BSA), using spectroscopic and molecular docking techniques. The fluorescence quenching measurements revealed that the quenching mechanism was static and the binding site of both Schiff bases to BSA was singular. Förster energy transfer measurements, synchronous fluorescence spectroscopy, and docking study showed both Schiff bases bind to the Trp residues of BSA in short distances. Docking study showed that both Schiff base molecules bind with BSA by forming several hydrogen and van der Waals bonds. In addition, molecular docking study indicated that Schiff base A and Schiff base B were located within the binding pocket of subdomain IB and subdomain IIA of BSA, respectively. Results of Fourier transform-infrared spectroscopy demonstrated that bovine serum albumin interacts with both Schiff bases and the secondary structure of BSA was changed.

Communicated by Ramaswamy H. Sarma     

Metal-catalyzed oxidation and cleavage of octopus glutathione transferase by the CU(II)-ascorbate system

Glutathione transferase (GST) from octopus hepatopancreas was rapidly inactivated by micromolar concentration of Cu(II) in the presence of ascorbate at neutral pH and 0°C. Omitting the metal ion or ascorbate, or replacing the Cu(II) with Fe(II) did not result in any inactivation. Glutathione or the conjugation product of glutathione and 1-chloro-2,4-dinitrobenzene offered complete protection of the enzyme from Cu(II)-induced inactivation. 1-Chloro-2,4-dinitrobenzene, however, did not provide any protection. The inactivation was time and Cu(II) concentration dependent. The dependence of inactivation rate on Cu(II) concentration displayed saturation kinetics, which suggests that the inactivation occurs in two steps with Cu(II) binding with the enzyme first (K_dCu = 260 μM), then the locally generated free radicals modify the essential amino acid residues in the active center, which results in enzyme inactivation. The Cu(II)-ascorbate system is, thus, an affinity reagent for the octopus GST. The enzyme inactivation was demonstrated to be followed by protein cleavage. Native octopus GST has a subunit M_r of 24,000. The inactivated enzyme was cleaved at the C-terminal domain (domain II) of the enzyme molecule and resulted in the formation of peptide fragment of M_r 15,300, which has the identical N-terminal amino acid sequence as the native enzyme. The other half of the peptide with M_r approximately 7700 was visible in the gels only after silver staining, which also revealed a minor cleavage site, also located at the domain II, to produce peptide fragments of M_r approximately 11,300 and 8300. The oxygen carrier molecule in the cephalopods' blood is the copper-containing hemocyanin, which during turnover will release Cu(II). Our results indicate that Cu(II) catalyzes a site-specific oxidation of the essential amino acid residues at the C-terminus of GST causing enzyme inactivation. The modified-enzyme is then affinity cleaved at the putative metal binding site. The ability of octopus GST to bind with free Cu(II) may have important biological implications to enable cephalopods to avoid copper-induced cellular toxicity.     

Fluorescence associated with the type 3 copper center of laccase

Laccases isolated from the lacquer tree Rhus vernicifera and the fungus Polyporus versicolor show fluorescence emission near 420 nm and phosphorescence emission in the 440–465 nm region. The fluorescence and phosphorescence excitation spectra for both laccases show maxima in the 315–330 nm range, a spectral region corresponding to the absorbance maxima for the type 3 binuclear Cu centers of the two enzymes. Additional evidence is presented for the association of the newly discovered emissions with the type 3 Cu centers of the two laccases.     

Effects of soil acidification and subsequent leaching on levels of extractable nutrients in a soil

Summary The effects of soil acidification (pH values from 6.5 to 3.8), and subsequent leaching, on levels of extractable nutrients in a soil were studied in a laboratory experiment. Below pH 5.5, acidification resulted in large increases in the amounts of exchangeable Al in the soil. Simultaneously, exchangeable cations were displayed from exchange sites and Ca, Mg, K and Na in soil solution increased markedly. With increasing soil acidification, increasing amounts of cations were leached; the magnitude of leaching loss was in the same order as the cations were present in the soil: Ca²⁺>Mg²⁺>K⁺>Na⁺. Soil acidification appeared to inhibit nitrification since in the unleached soils, levels of NO ₃ ⁻ clearly declined below pH 5.5 and at the same time levels of NH ₄ ⁺ increased greatly. Significant amounts of NH ₄ ⁺ and larger amounts of NO ₃ ⁻ , were removed from the soil during leaching. Concentrations of NaHCO₃-extractable phosphate remained unchanged between pH 4.3 and 6.0 but were raised at higher and lower pH values. No leaching losses of phosphate were detected. For the unleached soils, levels of EDTA-extractable Mn and Zn increased as the soil was acidified whilst levels of extractable Fe were first decreased and then increased greatly and those for Cu were decreased slightly between pH 6.5 and 6.0 and then unaffected by further acidification. Significant leaching losses of Mn and Zn were observed at pH values below 5.5 but losses of Fe were very small and those of Cu were not detectable.     

Mononuclear nickel(II) and copper(II) complexes with Schiff base ligands derived from 2,6-diformyl-4-methylphenol and S-methylisothiosemicarbazones

Four new square-planar Ni(II) and Cu(II) complexes with [N₂O₂] binding system were synthesized by metal-directed condensation of 2,6-diformyl-4-methylphenol with benzoyl or acetylacetone mono-S-methylisothiosemicarbazone. Only mononuclear “one-armed” complexes were obtained as a consequence of the different reactivity of the two carbonyl groups in the hydroxydialdehyde. The complexes were characterized by elemental analysis, EI MS and UV-Vis spectroscopy. The structural assignment was confirmed by X-ray diffraction analysis and NMR spectroscopy, for the Ni(II) complexes, and by ESR spectroscopy and magnetic measurements, for the Cu(II) complexes.     

Structural and surface patterning studies of N3-metalated adenine-copper complexes involving metal-olefin interaction

We report the synthesis, solid state structural characterization and direct surface patterning of two adenine-copper(I) complexes. The ligand, 9-allyladenine, exhibits Cu(I) coordination via an N3-M-N7 mode by invoking participation from an allylic double bond and acetonitrile solvent molecule to result in an EPR silent complex. Detailed crystal structure studies of the coordination polymer thus formed were followed by NMR to ascertain the Cu(I)-olefin interaction occurring via an allylic substituent at the N9 position. On air exposure, acetonitrile molecule was substituted by a water molecule affording a unique example of a water-bound Cu(I) complex. Direct deposition of these complexes on graphite surface resulted in a pattern which could be readily correlated to the crystal structure.     

高负载Cu单原子纳米酶的制备和类酶活性研究

目的 单原子纳米酶（single-atom nanozyme，SAN）因其高原子利用率及丰富的类酶活性被广泛研究。但是目前大多数SAN活性位点负载量较低，限制了其进一步应用和发展。本研究旨在制备一种高原子负载量的SAN，并对其类酶活性进行系统研究，希望为高负载SAN的制备提供思路，并为SAN在更广泛领域的应用提供理论支持。方法 本研究通过原位锚定策略将金属盐前驱体锚定在氨基化石墨烯量子点框架中，在惰性气体保护下进行高温热解稳定Cu原子和载体之间的化学键，制备出负载量高达7.66%（质量百分比）的高负载Cu单原子纳米酶（high-loading Cu SAN）。此外，以3,3",5,5"-四甲基联苯胺（TMB）和氮蓝四唑（NBT）为显色剂，评估了high-loading Cu SAN的类过氧化物酶（POD）、类氧化物酶（OXD）及类超氧化物歧化酶（SOD）活性，并与传统金属有机框架锚定法制备的低负载Cu单原子纳米酶（low-loading Cu SAN）作比较。以过氧化氢（H₂O₂）为催化底物，对比研究了高/低负载Cu SAN的类过氧化氢酶（CAT）活性。结果 研究表明，本文制备的高负载Cu SAN的类POD和SOD活性分别是低负载Cu SAN的3.4倍和8.88倍，且表现出类酶催化选择性。结论 本研究为高负载SAN的制备和活性研究提供了思路，为SAN在检测传感、疾病治疗以及环境保护等方面的应用奠定了基础。     

Antioxidative activity of copper in root nodules of yellow lupin plants

Copper nutrition inhibited lipid peroxidation in root nodules of yellow lupin plants at the early growth stages by about 50 %. The antioxidative activity of copper in the process of lipid peroxidation could be associated with Cu taking part in oxidative reaction of nodule catechol-like siderophores and its effect on iron accumulation and reactivity. The obtained results, for the first time, suggest that the ability of copper to inhibit lipid peroxidation in nodules could be considered as a major function for Cu requirements by symbiotic N₂ fixation in grain legume nodules.     

An EXAFS study of the copper accumulated by yeast cells

Summary X-ray absorption spectroscopy has been applied to the in vivo examination of copper-resistant yeast cells. The in vivo structure of the metal-binding site of the accumulated copper has been compared to that of the purified yeast thionein. Analysis of the EXAFS spectra performed on intact yeast cells indicates that the accumulated copper is univalent and is exclusively coordinated to sulfur atoms at a distance of 219 pin with an average coordination number of 2. In contrast, the purified protein indicates a univalent copper trigonally coordinated to sulfur at a distance of 221 pm. These discrepancies are discussed in terms of copper location in the resistant yeast cells.