Quantitative predictions for the chemiosmotic uptake of auxin

1. The predictions of a general kinetic model for the chemiosmotic uptake of auxin and other weak acids are compared with experimental results for the auxin indoleacetic acid. The proposed mechanism involves diffusional flux of undissociated acid, a saturable, voltage-sensitive flux of anion (A^-), and a carrier-mediated symport of H⁺ and A^-, all operating in parallel. During much of uptake, the electrochemical gradients are such that the net symport and the net anion flux are in opposition: the symport contributes more to influx; the anion path, to efflux. The voltage-sensitive flux of A^- therefore constitutes a leak. 2. The presence of a symport, whose carrier can distribute across the membrane in response to the internal and external concentrations of auxin, can speed the rate of uptake, but does not by itself alter the accumulation of auxin at equilibrium. 3. The accumulation ratio at equilibrium is less at low concentrations of auxin than at higher concentrations, indicating the presence of a saturable anion path. The concentration dependence of the transition depends on several factors, and is not a reliable indicator of the A^--carrier binding constant. 4. Observed uptake near neutral pH appears larger than is consistent with a voltage-sensitive anion flux being the only carrier-mediated path across the membrane. This observation provides indirect evidence for the presence of an auxin-proton symport in addition to a saturable A^- carrier. 5. The change in kinetics of uptake of [³H]indole-3-acetic acid (IAA), observed as the total concentration of IAA is raised from 0.1 to 100 M, is consistent with either (i) a symport that saturates at low concentrations, or (ii) activation of an A^- efflux by intermediate concentrations of auxin. 6. The data on the concentration dependence of uptake of auxin are not consistent with a multi-proton symport.Abbreviations A^- auxin anion - HA weak acid, particularly IAA - HXA carrier in electroneutral complex with a proton and the auxin anion - H₂XA carrier in electroneutral complex with two protons and the auxin anion - IAA indole-3-acetic acid - X auxin carrier - XA carrier-auxin anion complex     

Role of substrate binding forces in exchange-only transport systems: II. Implications for the mechanism of the anion exchanger of red cells

Summary The transition-state theory of exchange-only membrane transport is applied to experimental results in the literature on the anion exchanger of red cells. Two central features of the system are in accord with the theory: (i) forming the transition state in translocation involves a carrier conformational change; (ii) substrate specificity is expressed in transport rates rather than affinities. The expression of specificity is consistent with other evidence for a conformational intermediate (not the transition state) formed in the translocation of all substrates. The theory, in conjunction with concepts derived from the chemistry of macrocyclic ion inclusion complexes, prescribes certain essential properties in the transport site. Separate substites are required for the preferred substrates. Cl^– and HCO ₃ ^– , to account for tight binding in the transition state (K _diss1m). Further, the following mechanism is suggested. A substrate anion initially forms a loose surface complex at one subsite, but in the transition state the subsites converge to form an inclusion complex in which the binding forces are greatly increased through a chelation effect. The conformational change at the substrate site, which is driven by the mounting forces of binding, sets in train a wider conformational change that converts the carrier from an immobile to a mobile form. Though simple, this composite-site mechanism explains many unsual features of the system. It accounts for substrate inhibition, partially noncompetitive inhibition of one substrate by another, and tunneling, which is net transport under conditions where exchange should prevail, according to other models. All three types of behavior result from the formation of a ternary complex in which substrate anions are bound at both subsites. The mechanism also accounts for the enormous range of substrate structures accepted by the system, for the complex inhibition by the organic sulfate NAP-taurine, and for the involvement of several cationic side chains and two different protein domains in the transport site.     

Prolonged slow release of (Z)-11-hexadecenyl acetate employing polyurea microcapsules

Abstract:  The potential use of polyurea microcapsules, as 'release carriers' for insect pheromones, has been demonstrated. ( Z )-11-hexadecenyl acetate (Z11-16:Ac), the major sex pheromone component of several Noctuidae species, was used as the model molecule. The coating material's ability to release the pheromone was initially studied by the solid-phase micro-extraction technique. Polyurea microcapsules released Z11-16:Ac relatively slowly, with a duration of approximately 1 month, as it was determined under both laboratory and semi-field conditions. Preliminary laboratory bioassays revealed a satisfactory attraction of Sesamia males, at doses of 50 and 500 mg of dried microcapsules containing the aforementioned pheromone. Almost all male insects tested initiated flight and among them 40.2–49.4% successfully contacted the pheromone source. The preparation of polyurea microcapsules needs further refinement as to increase release duration; nevertheless, these results demonstrate strong potential for the future use of polyurea microcapsules as part of integrated insect control programmes.     

Endosperm enrichment and physicochemical properties of superior and inferior grain starch in super hybrid rice

• A significant asynchronous phenomenon exists in super hybrid rice because of the differences in spike and spikelet positions, which affect the accumulation and properties of starch. However, little is known about the endosperm enrichment and physicochemical properties of starch in superior and inferior grains in super hybrid rice.
• Rice YY2640 was selected as study material to investigate the enrichment and physicochemical properties of starch in superior and inferior grains in super rice using semi‐thin sections, X‐ray diffraction and related technologies.
• Superior grain filling was a continuous process, whereas inferior grain only started 8–10 days after anthesis. The order of starch accumulation starts in the central endosperm, then in the endosperm of the proximal vascular bundle and finally in the aleurone layer. Compared with the inferior grains, the superior grains have a higher 1000‐grain weight, apparent amylose content, total starch content, average starch granule size, relative crystallinity, solubility and a resonance peak ratio at 1022/995 cm^?1, whereas the swelling power and ratio of the resonance peak at 1045/1022 cm^?1 were lower. The final degree of hydrolysis of HCl, AAG and PPA of the superior grains were significantly lower than those of the inferior grains.
• The findings indicate that the different physicochemical properties of starch were mainly related to the development order of superior and inferior grains and the spatial enrichment of starch.

     

不同剂量右美托咪定辅助麻醉对老年结肠癌根治术患者麻醉效果和术后谵妄的影响及谵妄的相关因素分析

摘要 目的：探讨不同剂量右美托咪定辅助麻醉对老年结肠癌根治术患者麻醉效果,并分析术后谵妄的影响因素。方法：选取2019年4月~2021年1月期间我院收治的160例老年结肠癌根治术患者,根据随机数字表法将患者分为A组（53例）、B组（53例）和C组（54例）。A组和B组均于麻醉诱导前给予0.5 μg/kg右美托咪定,以0.2 μg/kg?h速率静脉输注至手术结束前30 min,A组术后镇痛时再给予右美托咪定0.05 μg/kg?h。C组给予等容量和等速率的生理盐水。观察三组的应激反应、麻醉效果、不良反应发生率、谵妄发生率。根据是否发生谵妄分为谵妄组（n=28）和无谵妄组（n=132）。采用Logistic回归分析术后谵妄的影响因素。结果：三组术后第3 d C反应蛋白（CRP）、白介素-6（IL-6）、多巴胺、肾上腺素均较手术结束升高（P<0.05）。A组、B组术后第3 d CRP、IL-6、多巴胺、肾上腺素低于C组（P<0.05）。A组、B组术后第3dCRP、IL-6、多巴胺、肾上腺素组间对比,无明显差异（P>0.05）。A组、B组、C组的不良反应总发生率组间的对比无明显差异（P>0.05）。B组的谵妄发生率明显低于A组、C组（P<0.05）。A组、C组谵妄发生率组间对比无明显差异（P>0.05）。单因素分析结果显示,术后谵妄的发生与年龄、术前抑郁、术前合并基础疾病数量、术中低氧血症、气腹后PaCO₂、白蛋白有关（P<0.05）。多因素Logistic回归分析结果显示：术前抑郁、年龄≥70岁、术前合并基础疾病数量≥3、术中低氧血症、气腹后PaCO₂偏高、白蛋白偏低是导致老年结肠癌根治术患者术后谵妄的危险因素（P<0.05）。结论：小剂量右美托咪定辅助麻醉可提高老年结肠癌根治术患者的麻醉效果,减少谵妄的发生率,同时术前抑郁、年龄≥70岁、术前合并基础疾病数量≥3、术中低氧血症、气腹后PaCO₂偏高、白蛋白偏低是引起谵妄发生的危险因素。     

The cysteine‐free single mutant C32S of APEX2 is a highly expressed and active fusion tag for proximity labeling applications

APEX2, an engineered ascorbate peroxidase for high activity, is a powerful tool for proximity labeling applications. Owing to its lack of disulfides and the calcium‐independent activity, APEX2 can be applied intracellularly for targeted electron microscopy imaging or interactome mapping when fusing to a protein of interest. However, APEX2 fusion is often deleterious to the protein expression, which seriously hampers its wide utility. This problem is especially compelling when APEX2 is fused to structurally delicate proteins, such as multi‐pass membrane proteins. In this study, we found that a cysteine‐free single mutant C32S of APEX2 dramatically improved the expression of fusion proteins in mammalian cells without compromising the enzyme activity. We fused APEX2 and APEX2^C32S to four multi‐transmembrane solute carriers (SLCs), SLC1A5, SLC6A5, SLC6A14, and SLC7A1, and compared their expressions in stable HEK293T cell lines. Except the SLC6A5 fusions expressing at decent levels for both APEX2 (70%) and APEX2^C32S (73%), other three SLC proteins showed significantly better expression when fusing to APEX2^C32S (69 ± 13%) than APEX2 (29 ± 15%). Immunofluorescence and western blot experiments showed correct plasma membrane localization and strong proximity labeling efficiency in all four SLC‐APEX2^C32S cells. Enzyme kinetic experiments revealed that APEX2 and APEX2^C32S have comparable activities in terms of oxidizing guaiacol. Overall, we believe APEX2^C32S is a superior fusion tag to APEX2 for proximity labeling applications, especially when mismatched disulfide bonding or poor expression is a concern.     

NMR evidence of a valinomycin-proton complex

In addition to the well-known complexes of valinomycin with alkali metal cations, an equimolar complex of the same compound with proton was found to be formed in nitrobenzene. Hydrogen bis(1,2-dicarbollylide) cobaltate (HDCC) was used as a proton source. According to NMR spectra, the complex formation is quantitative at proton/valinomycin molar ratios up to 1:1 but there is fast exchange of protons between coordinated and uncoordinated valinomycin molecules at lower ratios. 1H and 13C NMR spectra show a dramatic change in the valinomycin conformation during its coordination with protons, probably from a propeller-like to a bracelet-like form. As valinomycin is one of the well-known ion-carrying ionophores facilitating especially the K+ ion transport across a biological membrane, the existence of the valinomycin-proton complex could be important in biochemistry and biology.     

Protein-mediated energy-dissipating pathways in mitochondria

Mitochondrial production of reactive oxygen species (ROS) is a well-established fact of fundamental importance to aging and etiology of many pathologies with serious public health implications. The ROS production is an innate property of mitochondrial biochemistry inseparable from the oxidative metabolism. Recent discoveries indicate that in addition to several ROS-detoxifying enzyme systems, which remove ROS, mitochondria may also be able to limit their ROS production by the mechanism comprising several protein-mediated energy-dissipating ("uncoupling") pathways. Although the physiological significance and in vivo modus operandi of these pathways remain to be elucidated, several proteins potentially capable of energy dissipation are known. This mini-review addresses the identity of mitochondrial protein-mediated energy-dissipating pathways and the experimental evidence to their role in controlling ROS production.     

Binding of Paroxetine to the Serotonin Transporter in Membranes from Different Cells,Subcellular Fractions and Species

The binding of [³H]-paroxetine to membrane serotonin transporter (SERT) has been studied in membranes from different sources and subcellular fractions. From rat were membranes from venous blood platelets, brain total cortex, brain microsomes, brain crude and purified synaptosomes. Membranes were obtained from venous blood platelets from human volunteers and from brain cortex tissue from neurosurgery (cerebral lobectomies following craniocerebral injuries). The main finding was that the K _D of paroxetine binding to the SERT was the same for platelet and nerve ending (synaptosomal) membranes. That parameter was significantly lower in membranes from brain microsomes and cortex total tissue. No species related difference was found, where comparison was possible, between human and rat tissue. The equality of K _D of paroxetine binding to blood platelet membranes and to membranes from nerve endings appears to encourage the use of such membranes as a model for brain SERT. Binding at two different temperatures for several of the fractions suggests that paroxetine–SERT interaction is entropy-driven.