Methylglyoxal induces apoptosis in Jurkat leukemia T cells by activating c-Jun N-terminal kinase

Methylglyoxal (MG) is a physiological metabolite, but it is known to be toxic, inducing stress in cells and causing apoptosis. This study examines molecular mechanisms in the MG-induced signal transduction leading to apoptosis, focusing particularly on the role of JNK activation. We first confirmed that MG caused apoptosis in Jurkat cells and that it was cell type dependent because it failed to induce apoptosis in MOLT-4, HeLa, or COS-7 cells. A caspase inhibitor, Z-DEVD-fmk, completely blocked MG-induced poly(ADP-ribose)polymerase (PARP) cleavage and apoptosis, showing the critical role of caspase activation. Inhibition of JNK activity by a JNK inhibitor, curcumin, remarkably reduced MG-induced caspase-3 activation, PARP cleavage, and apoptosis. Stable expression of the dominant negative mutant of JNK also protected cells against apoptosis notably, although not completely. Correspondingly, loss of the mitochondrial membrane potential induced by MG was decreased by the dominant negative JNK. These results confirmed a crucial role of JNK working upstream of caspases, as well as an involvement of JNK in affecting the mitochondrial membrane potential.     

Peroxidation of proteins and lipids in suspensions of liposomes, in blood serum, and in mouse myeloma cells

There is growing evidence that proteins are early targets of reactive oxygen species, and that the altered proteins can in turn damage other biomolecules. In this study, we measured the effects of proteins on the oxidation of liposome phospholipid membranes, and the formation of protein hydroperoxides in serum and in cultured cells exposed to radiation-generated hydroxyl free radicals. Lysozyme, which did not affect liposome stability, gave 50% protection when present at 0.3 mg/ml, and virtually completely prevented lipid oxidation at 10 mg/ml. When human blood serum was irradiated, lipids were oxidized only after the destruction of ascorbate. In contrast, peroxidation of proteins proceeded immediately. Protein hydroperoxides were also generated without a lag period in hybrid mouse myeloma cells, while at the same time no lipid peroxides formed. These results are consistent with the theory that, under physiological conditions, lipid membranes are likely to be effectively protected from randomly-generated hydroxyl radicals by proteins, and that protein peroxyl radicals and hydroperoxides may constitute an important hazard to biological systems under oxidative stress.     

Flavonoids from Goodyera schlechtendaliana

A flavonol glycoside, 3-[[6-O-(6-deoxy-alpha-L-mannopyranosyl)-beta-D- glucopyranosyl]oxi]-5,7-dihydroxy-8-[(4-hydroxy-3,5-dimethoxyphenyl)meth yl]- 2-(3,4-dihydroxypheny)-4H-1-benzopyran-4-one, trivially named goodyerin, was isolated from the whole plant of Goodyera schlechtendaliana, along with three known flavonoids, rutin, kaempferol-3-O-rutinoside and isorhamnetin-3-O-rutinoside. The structures were established by spectroscopic analysis.     

The crystal structure of the penicillin-binding protein 2x from Streptococcus pneumoniae and its acyl-enzyme form: implication in drug resistance

Penicillin-binding proteins (PBPs), the primary targets for beta-lactam antibiotics, are periplasmic membrane-attached proteins responsible for the construction and maintenance of the bacterial cell wall. Bacteria have developed several mechanisms of resistance, one of which is the mutation of the target enzymes to reduce their affinity for beta-lactam antibiotics. Here, we describe the structure of PBP2x from Streptococcus pneumoniae determined to 2.4 A. In addition, we also describe the PBP2x structure in complex with cefuroxime, a therapeutically relevant antibiotic, at 2.8 A. Surprisingly, two antibiotic molecules are observed: one as a covalent complex with the active-site serine residue, and a second one between the C-terminal and the transpeptidase domains. The structure of PBP2x reveals an active site similar to those of the class A beta-lactamases, albeit with an absence of unambiguous deacylation machinery. The structure highlights a few amino acid residues, namely Thr338, Thr550 and Gln552, which are directly related to the resistance phenomenon.     

Involvement of Ca2+ in 1-Aminocyclopropane-1-Carboxylic Acid-Stimulated Pollen Germination

The role of 1-aminocyclopropane-1-carboxylic acid (ACC) in pollen germination was investigated in several plant species. It was found that ACC stimulated in vitro pollen germination in all five species of plants tested. EGTA and phenothiazine inhibited the increase in the germination rate induced by ACC. Free Ca²⁺ levels in the cytosol ([Ca²⁺]_cyt) in ungerminated and germinated pollen were 136 and 287 nm, respectively. Adding 0.25 mm ACC to the germination medium increased the [Ca²⁺]_cyt in germinated pollen up to 450 nm. When pollen was treated with both 0.25 mm ACC and 3.6 μm inositol 1,4,5-trisphosphate, the [Ca²⁺]_cyt increased to 850 nm, and pollen germination was also stimulated. In the presence of Li⁺, an inhibitor of inositol monophosphatase, the [Ca²⁺]_cyt was reduced to 155 nm, and the ACC-stimulated pollen germination was inhibited. The data provided evidence for the involvement of Ca²⁺ as a messenger in the stimulative effect of ACC on pollen germination. Received December 1, 1995; accepted February 18, 1998     

Complete assignment of 1H, 13C and 15N chemical shifts for bovine β-lactoglobulin: Secondary structure and topology of the native state is retained in a partially unfolded form

Although -lactoglobulin (-LG) has been studied extensively for more than 50 years, its physical properties in solution are not yet understood fully in terms of its three-dimensional (3D) structure. For example, despite a recent high-resolution crystal structure, it is still not clear why the two common variants of bovine -LG which differ by just two residues have different aggregation properties during milk processing. We have conducted solution-state NMR studies on a recombinant form of the A variant of -LG at low pH conditions where the protein is partially unfolded and exists as a monomer rather than a dimer. Using a¹³ C,¹⁵N-labelled sample, expressed in Pichia pastoris, we have employed the standard combination of 3D heteronuclear NMR techniques to obtain near complete assignments of proton, carbon and nitrogen resonances. Using a novel pulse sequence we were able to obtain additional assignments, in particular those of methyl groups in residues preceding proline within the sequence. From chemical shifts and on the basis of inter-residue NOEs, we have inferred the secondary structure and topology of monomeric -LG A. It includes eight antiparallel -strands arranged in a barrel, flanked by an -helix, which is typical of a member of the lipocalin family. A detailed comparison with the crystal structure of the dimeric form (for a mixture of A and B variants) at pH 6.5 reveals a close resemblance in both secondary structure and overall topology. Both forms have a ninth -strand which, at the higher pH, forms part of the dimer interface. These studies represent the first full NMR assignment of -LG and will form the basis for a complete characterisation of the solution structure and dynamics of this protein and its variants.     

龙胆VA菌根真菌的分离和鉴定

采用湿筛法和单孢接种技术,从东北龙胆根际土壤中分离到能在东北龙胆组培苗上形成VA菌根的真菌孢子和孢子果呆,依其显微形态特征对部分菌株进行鉴定,大多属于球囊霉属（Glomus）中的漏斗孢球囊霉（Glomusmosseae）和地球囊霉（G．geosporum）     

红三叶人工草地营养元素的生物循环

 本文研究了我国北亚热带高海拔地区红三叶人工草地11种营养元素的生物循环特征。结果表明:1.营养元素的存留量、归还量和吸收量均可分为5个水平;(1)高量级：氮、钾、钙;(2)中量级：磷、镁;(3)低量级：铁;(4)少量级：锰、锌、铜、硼;(5)微量级：钼。2．红三叶群落地上部的净生产量、自然归还量和元素的存留量均显著高于地下部。3．红三叶人工草地的元素输出量以氮、钾、钙较大。此外,对草用和种用红三叶群落营养元素生物循环特征的差异进行了比较。为维持本区红三叶人工草地营养元素的平衡,目前必须施用磷肥,施用量不能小于250kg·hm-2过磷酸钙。     

The chemistry of rhenium and technetium. Part III. The synthesis and characterisation of oxo-bis-(tetrathiomolybdenato)-technetium(V) and its reduction by triphenylphosphine

The Complexes (Bu₄N)[TcO(MoS₄)₂] and Tc- (PPh₃)₂(MoS₄)₂ were prepared. The former complex has a much lower Tc-O stretching frequency than is generally found gor the TcO³⁺. moiety. The latter technetium(IV) Complex was obtained by the reduction of Tc^(v) O(MoS₄)₂^? with triphenylphosphine and also by the substitution reaction of TcCl₄(PPh₃)2 with MoS₄^2-. Previous reductions of this nature have led to the isolation of species that differ by two formal oxidation state numbers from the oxidant.