玉米地膜制种促熟增产的生理学机理

系统地探讨了玉米地膜制种促熟增产的作物生理学机理．结果表明,玉米池膜制种可以改善土壤水温条件、增强植株根系活力和群体光合作用性能、促进植株生长发育和光合产物的积累与分配．为该技术应用提供了科学依据．     

On Dioxygen and Substrate Access to Soluble Methane Monooxygenases: An all‐Atom Molecular Dynamics Investigation in Water Solution

In a preliminary exploration of the dummy model for diiron proteins, random‐acceleration molecular dynamics (RAMD) revealed that a pure four‐helix bundle structure, like hemerythrin, constitutes an efficient cage for dioxygen (O₂), which can only leave from defined, albeit very broad, gates. However, this well ordered structure does not constitute an archetype on which to compare O₂ permeation of other diiron proteins, like the complex of soluble methane monooxygenase hydroxylase with the regulatory protein (sMMOH‐MMOB). The reason is that with this complex, unlike hemerythrin, the four helices of the four‐helix bundle are heavily bent, and RAMD showed that most traps for O₂ lie outside them. It was also observed that, in spite of a nearly identical van der Waals radius for O₂ and the natural substrate CH₄, the latter behaves under RAMD as a bulkier molecule than O₂, requiring a higher external force to be brought out of sMMOH‐MMOB along trajectories of viable length. All that determined with sMMOH‐MMOB multiple gates and multiple pathways to each of them through several binding pockets, for both O₂ and CH₄. Of the two equally preferred pathways for O₂, at right angle with one another, one proved to be in accordance with the Xe‐atom mapping for sMMOH. In contrast, none of the pathways identified for CH₄ proved to be in accordance with such mapping, CH₄ looking for more open avenues instead.     

Gait and posture discrimination in sheep using a tri-axial accelerometer

Temporo-spatial observation of the leg could provide important information about the general condition of an animal, especially for those such as sheep and other free-ranging farm animals that can be difficult to access. Tri-axial accelerometers are capable of collecting vast amounts of data for locomotion and posture observations; however, interpretation and optimization of these data records remain a challenge. The aim of the present study was to introduce an optimized method for gait (walking, trotting and galloping) and posture (standing and lying) discrimination, using the acceleration values recorded by a tri-axial accelerometer mounted on the hind leg of sheep. The acceleration values recorded on the vertical and horizontal axes, as well as the total acceleration values were categorized. The relative frequencies of the acceleration categories (RFACs) were calculated in 3-s epochs. Reliable RFACs for gait and posture discrimination were identified with discriminant function and canonical analyses. Post hoc predictions for the two axes and total acceleration were conducted, using classification functions and classification scores for each epoch. Mahalanobis distances were used to determine the level of accuracy of the method. The highest discriminatory power for gait discrimination yielded four RFACs on the vertical axis, and five RFACs each on the horizontal axis and total acceleration vector. Classification functions showed the highest accuracy for walking and galloping. The highest total accuracy on the vertical and horizontal axes were 90% and 91%, respectively. Regarding posture discrimination, the vertical axis exhibited the highest discriminatory power, with values of RFAC (0, 1]=99.95% for standing; and RFAC (−1, 0]=99.50% for lying. The horizontal axis showed strong discrimination for the lying side of the animal, as values were in the acceleration category of (0, 1] for lying on the left side and (−1, 0] on the right side. The algorithm developed by the method employed in the present study facilitates differentiation of the various types of gait and posture in animals from fewer data records, and produces the most reliable acceleration values from only one axis within a short time frame. The present study introduces an optimized method by which the tri-axial accelerometer can be used in gait and posture discrimination in sheep as an animal model.     

Accelerating patient access to novel biologics using stable pool‐derived product for non‐clinical studies and single clone‐derived product for clinical studies

Cell cloning and subsequent process development activities are on the critical path directly impacting the timeline for advancement of next generation therapies to patients with unmet medical needs. The use of stable cell pools for early stage material generation and process development activities is an enabling technology to reduce timelines. To successfully use stable pools during development, it is important that bioprocess performance and requisite product quality attributes be comparable to those observed from clonally derived cell lines. To better understand the relationship between pool and clone derived cell lines, we compared data across recent first in human (FIH) programs at Amgen including both mAb and Fc‐fusion modalities. We compared expression and phenotypic stability, bioprocess performance, and product quality attributes between material derived from stable pools and clonally derived cells. Overall, our results indicated the feasibility of matching bioprocess performance and product quality attributes between stable pools and subsequently derived clones. These findings support the use of stable pools to accelerate the advancement of novel biologics to the clinic. © 2017 The Authors Biotechnology Progress published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers Biotechnol. Prog., 33:1476–1482, 2017     

Ligand Entry and Exit Pathways in the β2-Adrenergic Receptor

The recently determined crystal structure of the human β₂-adrenergic (β₂AR) G-protein-coupled receptor provides an excellent structural basis for exploring β₂AR-ligand binding and dissociation process. Based on this crystal structure, we simulated ligand exit from the β₂AR receptor by applying the random acceleration molecular dynamics (RAMD) simulation method. The simulation results showed that the extracellular opening on the receptor surface was the most frequently observed egress point (referred to as pathway A), and a few other pathways through interhelical clefts were also observed with significantly lower frequencies. In the egress trajectories along pathway A, the D192-K305 salt bridge between the extracellular loop 2 (ECL2) and the apex of the transmembrane helix 7 (TM7) was exclusively broken. The spatial occupancy maps of the ligand computed from the 100 RAMD simulation trajectories indicated that the receptor-ligand interactions that restrained the ligand in the binding pocket were the major resistance encountered by the ligand during exit and no second barrier was notable. We next performed RAMD simulations by using a putative ligand-free conformation of the receptor as input structure. This conformation was obtained in a standard molecular dynamics simulation in the absence of the ligand and it differed from the ligand-bound conformation in a hydrophobic patch bridging ECL2 and TM7 due to the rotation of F193 of ECL2. Results from the RAMD simulations with this putative ligand-free conformation suggest that the cleft formed by the hydrophobic bridge, TM2, TM3, and TM7 on the extracellular surface likely serves as a more specific ligand-entry site and the ECL2-TM7 hydrophobic junction can be partially interrupted upon the entry of ligand that pushes F193 to rotate, resulting in a conformation as observed in the ligand-bound crystal structure. These results may help in the design of β₂AR-targeting drugs with improved efficacy, as well as in understanding the receptor subtype selectivity of ligand binding in the β family of the adrenergic receptors that share almost identical ligand-binding pockets, but show notable amino acid sequence divergence in the putative ligand-entry site, including ECL2 and the extracellular end of TM7.     

Pitch then power: limitations to acceleration in quadrupeds

Rapid acceleration and deceleration are vital for survival in many predator and prey animals and are important attributes of animal and human athletes. Adaptations for acceleration and deceleration are therefore likely to experience strong selective pressures—both natural and artificial. Here, we explore the mechanical and physiological constraints to acceleration. We examined two elite athletes bred and trained for acceleration performance (polo ponies and racing greyhounds), when performing maximal acceleration (and deceleration for ponies) in a competitive setting. We show that maximum acceleration and deceleration ability may be accounted for by two simple limits, one mechanical and one physiological. At low speed, acceleration and deceleration may be limited by the geometric constraints of avoiding net nose-up or tail-up pitching, respectively. At higher speeds, muscle power appears to limit acceleration.     

Molecular Dynamics Simulation of Dioxygen Pathways through Mini Singlet Oxygen Generator (miniSOG), a Genetically Encoded Marker and Killer Protein

In this work, molecular dynamics (MD) simulations of the permeation of proteins by small gases of biological significance have been extended from gas carrier, sensor, and enzymatic proteins to genetically encoded tags and killer proteins. To this end, miniSOG was taken as an example of current high interest, using a biased form of MD, called random‐acceleration MD. Various egress gates and binding pockets for dioxygen, as an indistinguishable mimic of singlet dioxygen, were found on both above and below the isoalloxazine plane of the flavin mononucleotide cofactor in miniSOG. Of such gates and binding pockets, those lying within two opposite cones, coaxial with a line normal to the isoalloxazine plane, and with the vertex at the center of such a plane are those most visited by the escaping gas molecule. Out of residues most capable of quenching ¹O₂, Y30, lying near the base of one such a cone, and H85, near the base of the opposite cone, are held to be most responsible for the reduced quantum yield of ¹O₂ with folded miniSOG with respect to free flavin mononucleotide in solution.     

Nonheterochronic developmental changes underlie morphological heterochrony in the evolution of the Ardeidae

Evolutionary changes in developmental timing and rates (heterochrony) are a source of morphological variation. Here we explore a central issue in heterochronic analysis: are the alterations in developmental timing and rates the only factor underlying morphological heterochrony? Tarsometatarsal growth through endochondral ossification in Ardeidae evolution has been taken as a case study. Evolutionary changes in bone growth rate (morphological heterochrony) might be either (a) the result of alterations in the mitotic frequency of epiphyseal chondrocytes (process‐heterochrony hypothesis), or (b) the outcome of alterations in the number of proliferating cells or in the size of hypertrophic chondrocytes (structural hypothesis). No correlation was found between tarsometatarsal growth rates and the frequency of cell division. However, bone growth rates were significantly correlated with the number of proliferating cells. These results support the structural hypothesis: morphological acceleration and deceleration are the outcome of evolutionary changes in one structural variable, the number of proliferating cells.     

功能性心电图的基本特征及其产生机理

本文概述了航空、航天应激心电图(高空急性缺氧,加压供氧、加速度,失重,高温、下身负压与爆炸减压)、运动员与飞行员以及普通工作人员的非病理性心电图。此类心电图的形态改变同病理性心电图有同有异。各波段有意义的改变主要是P波与ST-T异常,心律失常中主动性异位节律、窦房结节律失常与被动性异位节律以及传导异常均可见。产生机理属于反射性或中枢性;诱因与产生机理均属功能性质。我们主张将此类异常心电图称为功能性心电图,以资区别于病理性心电图,利于科研中正确评价人体反应以及临床上鉴别诊断。