Tyrosine transport by membrane vesicles isolated from rat brain

Tyrosine uptake by membrane vesicles derived from rat brain has been investigated. The uptake is dependent on an Na⁺ gradient ([$\text{Na}{}^{\mathrm{+}}\text{]}\text{outside}\text{> [}\text{Na}{}^{\mathrm{+}}\text{]}\text{inside}$). The uptake is transport into an osmotically active space and not a binding artifact as indicated by the effect of increasing the medium osmolarity. The process is stimulated by a membrane potential (negative inside) as demonstrated by the effect of the ionophores valinomycin and carbonyl cyanide $\text{m-}\text{chlorophenylhydrazone}$ and anions with different permeabilities. Kinetic data show that tyrosine is accumulated by two systems with different affinities. Tyrosine uptake is inhibited by the presence of phenylalanine and tryptophan.     

The photoreaction center of Rhodospirillum rubrum mutant strain F24.1

Rhodospirillum rubrum strain F24.1 is a spontaneous revertant of nonphototrophic mutant F24 derived from wild-type strain S1. Strain F24 shows no detectable photochemical activity and contains, at most, traces of the photoreaction center polypeptides. Strain F24.1 has a phototrophic growth rate close to that of the wild-type strain (Picorel, R., del Valle-Tascón, S. and Ramírez, J.M. (1977) Arch. Biophys. Biochem. 181, 665–670) but shows little photochemical activity. Light-induced absorbance changes in the near-infrared, photoinduced EPR signals and ferricyanide-elicited absorbance changes indicate that strain F24.1 has a photoreaction center content of 7–8% as compared to strain S1. Polyacrylamide gel electrophoresis of isolated F24.1 chromatophores shows the photoreaction center polypeptides to be present in amounts compatible with this value. Photoreaction center was prepared from strain F24.1 and showed no detectable difference with that of strain S1. It is concluded that strain F24.1 photosynthesis is due entirely to its residual 7–8% of typical photoreaction center.     

Biosynthesis of candicidin by phosphate-limited resting cells ofStreptomyces griseus

Summary A phosphate-limited resting cell system ofStreptomyces griseus in a synthetic medium has been developed in which biosynthesis of the polyene macrolide, candicidin, is linear for at least 36 h without cell growth. Glucose and to a lesser degree sucrose, but not lactose, support antibiotic synthesis. Glucose is utilized at a constant rate for antibiotic synthesis without affecting mycelial dry weight. Acetate and propionate, the building units of the macrolide aglycone, stimulate candicidin biosynthesis in cultures supplemented with glucose but do not support its synthesis in the absence of glucose. Maximal stimulation of candicidin biosynthesis was produced by 40 mM propionate or 250 mM acetate. The biosynthetic intermediate, methyl malonate, and the analog, 1-propanol, were more stimulatory than propionate at the same concentration.     

Properties of spinach chloroplast fructose-1,6-diphosphatase

Photosynthetic fructose-1,6-diphosphatase (FDPase) fractions I and II, earlier purified from spinach leaves, show a similar amino acid composition, with the exception of a higher glutamic acid content in the latter. In both fractions glutamic and aspartic acids are the main amino acids. pH activity profiles of fractions I and II are similar, with optima at 8·65–8·70, both showing a high specificity for fructose- 1,6-diphosphate. These two fractions are Mg²⁺-dependent for activity, with an Optimum Mg²⁺ concentration of 10 mM in standard conditions, which shifts to 5 mM when the MG²⁺/EDTA ratio is increased to 10; Mn²⁺ and Co²⁺ are slightly active. EDTA enhances FDPase activity slightly, with an optimum at 0·4–0·8 mM. Cysteine has no activating effect, and acts as an inhibitor above 10 mM. Both I and II have an optimum substrate concentration of 4 mM, and the substrate inhibits at concns above this value. Kinetic velocity curves are sigmoidal, with the concave zone located in the range of physiological substrate concns. (Hill coefficient 1·75 for both). This suggests a strong regulatory role of fructose-1,6-diphosphate. K_m values are 1·4 × 10⁻³ M (fraction I) and 1·1 × 10⁻³ M (fraction II). The highest activity rate occurs at 60°, in accordance with the high thermostability of both fractions; the activation energies are 14·3 kcal/mol (fraction I) and 13·0 kcal/mol (fraction II).     

The control by respiration of the uptake of α-methyl glucoside in Escherichia coli K12

The uptake of methyl α-d-glucopyranoside (α-MG) by Escherichia coli K12 was decreased by the addition of substrates which stimulated the rate of oxygen consumption by the cells. The inhibition, which occurred only at non-saturating concentrations of α-MG, was not the result of a stimulation of the rate of exit of intracellular α-MG, and was abolished by the presence of carbonyl cyanide m-chlorophenylhydrazone or sodium azide. Since those drugs inhibit energy conservation at the respiratory chain and did not alter significantly the rate of oxygen consumption under the conditions for the assay of α-MG uptake, it appears that the inhibition of the transport system by respirable substrates is mediated by some form of energy derived from respiration.     

长三角城市群城市洪涝韧性与生态系统服务的耦合协调关系

厘清城市洪涝韧性与生态系统服务之间耦合协调关系,可为城市防洪减灾和生态文明建设提供重要决策参考。综合运用基于麻雀算法的投影寻踪模型、InVEST模型和耦合协调度模型,在分析2000-2020年长三角城市群的城市洪涝韧性与水源涵养、水质净化、土壤保持和气候调节四种生态系统服务时空格局基础上,尝试探索两者耦合协调关系及其时空演变特征。研究发现:(1)长三角城市群的城市洪涝韧性水平呈现"N"型增加趋势,并呈现"上海>江苏>浙江>安徽"的空间格局,表明经济水平越高的城市展现出更强的洪涝韧性,经济是影响城市洪涝韧性波动的主要因素,而自然韧性成为城市洪涝韧性提升的关键短板;(2)生态系统服务存在显著的空间异质性,高植被覆盖的南部地区提供了更高的生态系统服务,从时间维度看其空间分布是稳定的,水源涵养和水质净化服务总体呈向好趋势,土壤保持服务整体呈现倒"N"型增加,气候调节服务呈现微弱的下降趋势;(3)城市洪涝韧性与生态系统服务的耦合协调度在研究期内较为稳定,且与生态系统服务的时空变化趋于一致,呈现"南高北低、由西南向东北逐渐减弱"的趋势,生态系统服务较高的城市,表现出更好的耦合协调性,且随着生态系统服务的增加而改善。因此,长三角城市群有必要从提高生态系统服务功能的角度出发,因地制宜、分类施策,促进城市洪涝韧性与生态系统服务的协调发展。     

A role for the Saccharomyces cerevisiae Rtt109 histone acetyltransferase in R-loop homeostasis and associated genome instability

The stability of the genome is occasionally challenged by the formation of DNA–RNA hybrids and R-loops, which can be influenced by the chromatin context. This is mainly due to the fact that DNA–RNA hybrids hamper the progression of replication forks, leading to fork stalling and, ultimately, DNA breaks. Through a specific screening of chromatin modifiers performed in the yeast Saccharomyces cerevisiae, we have found that the Rtt109 histone acetyltransferase is involved in several steps of R-loop-metabolism and their associated genetic instability. On the one hand, Rtt109 prevents DNA–RNA hybridization by the acetylation of histone H3 lysines 14 and 23 and, on the other hand, it is involved in the repair of replication-born DNA breaks, such as those that can be caused by R-loops, by acetylating lysines 14 and 56. In addition, Rtt109 loss renders cells highly sensitive to replication stress in combination with R-loop-accumulating THO-complex mutants. Our data evidence that the chromatin context simultaneously influences the occurrence of DNA–RNA hybrid-associated DNA damage and its repair, adding complexity to the source of R-loop-associated genetic instability.     

采自云南热带雨林的中国多孔菌两新记录种

<正>1 INTRODUCTION Wood-rotting fungi have been intensively studied in China (Dai & Niemel? 2002; Dai et al. 2003, 2004a, 2004b; Dai & Penttil? 2006), and some new species and new records were found from     

Effects of highly selective sensory/motor nerve injury on bone metabolism and bone remodeling in rats

Objectives:This work aimed to investigate the mechanism of selective sensory/motor nerve injury in affecting bone metabolism and remodeling.Methods:The selective sensory/motor nerve injury rat model was constructed through posterior rhizotomy (PRG), anterior rhizotomy (ARG), or anterior combined with posterior rhizotomy (APRG) at the L_4-6 sensory/motor nerves on the right side of rats. Sham-operated (SOG) rats served as control. At 8 weeks after surgery, the sciatic nerves, spinal cord segments L₅ and tibial tissues were collected for analysis.Results:the integrity of trabecular bone was damaged, the number of trabecular bone was decreased and the number of osteoclasts were increased in ARG group. ARG activated NF-κβ and PPAR-γ pathways, and inhibited Wnt/β-catenin pathway. ARG group exhibited high turnover bone metabolism. In PRG group, the trabecular bone morphology became thinner, and the number of osteoclasts was increased. NF-κβ pathway was activated and OPG/RANKL ratio was decreased in PRG group. The activated osteoclasts, reduced osteoblasts activity and lower turnover bone metabolism were observed in PRG group. Additionally, the bone metabolism in APRG group was similar to ARG group.Conclusion:The posterior rhizotomy and anterior rhizotomy induced the different degree of osteoporosis in rats, which may attribute to regulate Wnt/β-catenin, NF-κβ and PPAR-γ signalling pathways.