Isokinetic Relationship in the Oxidation of Cuprous Stellacyanin by Cobalt(III) Complexes

Rate parameters have been obtained for the oxidation of cuprous stellacyanin by cobalt(III) ions of the form cis(N)-[CoN₂O₄]^?, including cis(N)-[Co(NTA)(gly)]^?, cis(N)-[Co(IDA)₂]^?, [Co(en)(ox)₂]^?(μ 0.5 M(phosphate), pH 7.0), and Co(EDTA)^?(μ 0.1 M(NaCl), pH 7.2, 0.001 M phosphate). An excellent isokinetic correlation between the activation parameters ΔH^≠ and ΔS^≠ exists for the reactions of aminopolycarboxylatocobalt(III) ions with reduced stellacyanin (β = 300 ± 12 K; correlation coefficient = 0.995). It is concluded that enthalpy-entropy compensation in these reactions may be understood in terms of differing orientations preferred by the various oxidants in forming precursor complexes with the reduced blue protein. While ΔH^≠ and ΔS^≠ values for electron transfer from stellacyanin to cis(N)-[CoN₂O₄]^? ions vary over ranges of 10.7 kcal/mol and 34 cal/mol-deg, respectively, room temperature rate constants are relatively constant (3.6–34.5 M^?1 sec^?1), as expected from Marcus theory for outer sphere electron transfer.     

Vascular plant one-zinc finger 1 (VOZ1) and VOZ2 negatively regulate phytochrome B-mediated seed germination in Arabidopsis

ABSTRACT

Seed germination is regulated by light. Phytochromes (Phys) act as red and far-red light photoreceptors to mediate seed germination. However, the mechanism of this process is not well understood. In this study, we found that the Arabidopsis thaliana mutants vascular plant one-zinc finger 1 (voz1) and voz2 showed higher seed germination percentage than wild type when PhyB was inactivated by far-red light. In wild type, VOZ1 and VOZ2 expression were downregulated after seed imbibition, repressed by PhyB, and upregulated by Phytochrome-interacting factor 1 (PIF1), a key negative regulator of seed germination. Red light irradiation and the voz1voz2 mutation caused increased expression of Gibberellin 3-oxidase 1 (GA3ox1), a gibberellin (GA) biosynthetic gene. We also found that VOZ2 is bound directly to the promoter of GA3ox1 in vitro and in vivo. Our findings suggest that VOZs play a negative role in PhyB-mediated seed germination, possibly by directly regulating GA3ox1 expression.     

Evolutionary analysis of three gibberellin oxidase genes in rice, Arabidopsis, and soybean

GAs are plant hormones that play fundamental roles in plant growth and development. GA2ox, GA3ox, and GA20ox are three key enzymes in GA biosynthesis. These enzymes belong to the 2OG-Fe (II) oxygenase superfamily and are independently encoded by different gene families. To date, genome-wide comparative analyses of GA oxidases in plant species have not been thoroughly carried out. In the present work, 61 GA oxidase family genes from rice (Oryza sativa), Arabidopsis, and soybean (Glycine max) were identified and a full study of these genes including phylogenetic tree construction, gene structure, gene family expansion and analysis of functional motifs was performed. Based on phylogeny, most of the GA oxidases were divided into four subgroups that reflected functional classifications. Intron/intron average length of GA oxidase genes in rice analysis revealed that GA oxidase genes in rice experienced substantial evolutionary divergence. Segmental duplication events were mainly found in soybean genome. However, in rice and Arabidopsis, no single expansion pattern exhibited dominance, indicating that GA oxidase genes from these species might have been subjected to a more complex evolutionary mechanism. In addition, special functional motifs were discovered in GA20ox, GA3ox, and GA2ox, which suggested that different functional motifs are associated with differences in protein function. Taken together our results suggest that GA oxidase family genes have undergone divergent evolutionary routes, especially at the monocot-dicot split, with dynamic evolution occurring in Arabidopsis thaliana and soybean.     

Two reaction pathways for transformation of high potential cytochrome b559 of PS II into the intermediate potential form

This study describes an analysis of different treatments that influence the relative content and the midpoint potential of HP Cyt b559 in PS II membrane fragments from higher plants. Two basically different types of irreversible modification effects are distinguished: the HP form of Cyt b559 is either predominantly affected when the heme group is oxidized (“O-type” effects) or when it is reduced (“R-type” effects). Transformation of HP Cyt b559 to lower potential redox forms (IP and LP forms) by the “O-type” mechanism is induced by high pH and detergent treatments. In this case the effects consist of a gradual decrease in the relative content of HP Cyt b559 while its midpoint potential remains unaffected. Transformation of HP Cyt b559 via an “R-type” mechanism is caused by a number of exogenous compounds denoted L: herbicides, ADRY reagents and tetraphenylboron. These compounds are postulated to bind to the PS II complex at a quinone binding site designated as Q_C which interacts with Cyt b559 and is clearly not the Q_B site. Binding of compounds L to the Q_C site when HP Cyt b559 is oxidized gives rise to a gradual decrease in the E_m of HP Cyt b559 with increasing concentration of L (up to 10 K_ox(L) values) while the relative content of HP Cyt b559 is unaffected. Higher concentrations of compounds L required for their binding to Q_C site when HP Cyt b559 is reduced (described by K_red(L)) induce a conversion of HP Cyt b559 to lower potential redox forms (“R-type” transformation). Two reaction pathways for transitions of Cyt b559 between the different protein conformations that are responsible for the HP and IP/LP redox forms are proposed and new insights into the functional regulation of Cyt b559 via the Q_C site are discussed.     

The conserved regulation of mitochondrial uncoupling proteins: From unicellular eukaryotes to mammals

Uncoupling proteins (UCPs) belong to the mitochondrial anion carrier protein family and mediate regulated proton leak across the inner mitochondrial membrane. Free fatty acids, aldehydes such as hydroxynonenal, and retinoids activate UCPs. However, there are some controversies about the effective action of retinoids and aldehydes alone; thus, only free fatty acids are commonly accepted positive effectors of UCPs. Purine nucleotides such as GTP inhibit UCP-mediated mitochondrial proton leak. In turn, membranous coenzyme Q may play a role as a redox state-dependent metabolic sensor that modulates the complete activation/inhibition of UCPs. Such regulation has been observed for UCPs in microorganisms, plant and animal UCP1 homologues, and UCP1 in mammalian brown adipose tissue. The origin of UCPs is still under debate, but UCP homologues have been identified in all systematic groups of eukaryotes. Despite the differing levels of amino acid/DNA sequence similarities, functional studies in unicellular and multicellular organisms, from amoebae to mammals, suggest that the mechanistic regulation of UCP activity is evolutionarily well conserved. This review focuses on the regulatory feedback loops of UCPs involving free fatty acids, aldehydes, retinoids, purine nucleotides, and coenzyme Q (particularly its reduction level), which may derive from the early stages of evolution as UCP first emerged.     

牛眼透明质酸的分离及性质测定

研究了牛眼透明质酸(HA)的提纯方法,采用0.125 mol/L Na₂SO₄取代0.1 mol/L NaCl溶解粗品,发现前者溶解液中有2个组分,一个组分被十六烷基溴代吡啶(CBP)吸附回收,产物呈纤维状,另一组分保留在溶液中并能通过分级稀释而被沉淀回收,产物呈粉末状;而用0.1 mol/ml NaCl溶解粗品,除了被CBP吸附回收外,保留在溶液中的HA不能被回收;与同类方法相比,回收率提高1.7倍以上.还分析了产物的性质,与同类样品比较,提高了纯度,降低了提纯中有机溶剂的消耗.     

拟南芥GA2ox基因家族启动子分析

赤霉素是一类重要的植物激素,它参与调节植物生长发育的各个阶段。真核基因的表达受多种因素的调控,其中启动子在转录水平上的调节作用至关重要,但是目前对拟南芥GA2ox基因家族上游顺式元件的详细分析较少。本研究分析了AtGA2ox基因家族染色体定位、进化关系、蛋白模体以及顺式元件。分析结果表明：AtGA2ox基因家族分为2个亚类;具有相对集中的染色体分布：具有相似的内含子和外显子结构;AtGA2ox基因家族成员进化关系越相近,模体和顺式元件则越保守且分布位置更接近。PLACE和Plant CARE以及DMB分析显示,AtGA2ox基因家族存在许多保守元件,受多因素的调控,在此家族的上游调控区域普遍存在组织和器官特异性表达元件、光响应元停、激素响应元件以及其他环境响应元件。基因表达谱分析结果表明,在激素诱导下,AtGA2ox基因家族均有响应。这些元件不仅作为正调控元件,诱导部分AtGA2ox基因的表达,而且还能作为负调控元件．抑制其他AtGA2ox基因的表达。     

Therio-ontology: A personal view of 40 years of farm animal embryo form and function

The main purpose of this autobiographical reminiscence of 40 years of embryo research is to provide young theriogenologists with a firsthand account of how career development can depend strongly on early influences that become modified by changing circumstances. With no intention of being didactic, I hope that my experience of coping with enormous changes in techniques and attitudes may be of use to some of those embarking on a further 40 years of change of at least equal enormity.