Dynamic interactions between arterial pressure and sympathetic nerve activity: role of arterial baroreceptors

The role of arterial baroreceptors in controlling arterial pressure (AP) variability through changes in sympathetic nerve activity was examined in conscious rats. AP and renal sympathetic nerve activity (RSNA) were measured continuously during 1-h periods in freely behaving rats that had been subjected to sinoaortic baroreceptor denervation (SAD) or a sham operation 2 wk before study (n = 10 in each group). Fast Fourier transform analysis revealed that chronic SAD did not alter high-frequency (0.75-5 Hz) respiratory-related oscillations of mean AP (MAP) and RSNA, decreased by approximately 50% spectral power of both variables in the midfrequency band (MF, 0.27-0.74 Hz) containing the so-called Mayer waves, and induced an eightfold increase in MAP power without altering RSNA power in the low-frequency band (0.005-0.27 Hz). In both groups of rats, coherence between RSNA and MAP was maximal in the MF band and was usually weak at lower frequencies. In SAD rats, the transfer function from RSNA to MAP showed the characteristics of a second-order low-pass filter containing a fixed time delay ( approximately 0.5 s). These results indicate that arterial baroreceptors are not involved in production of respiratory-related oscillations of RSNA but play a major role in the genesis of synchronous oscillations of MAP and RSNA at the frequency of Mayer waves. The weak coupling between slow fluctuations of RSNA and MAP in sham-operated and SAD rats points to the interference of noise sources unrelated to RSNA affecting MAP and of noise sources unrelated to MAP affecting RSNA.     

Identifying interactions between genes and early environment in the mouse

Interactions between genetic and early environmental factors are recognized to play a critical role in modulating susceptibility to disease, particularly mental illness. In order to better understand such mechanisms at the molecular level, we have developed a screening paradigm in mice that allows us to test the ability of targeted mutations in candidate genes to modify susceptibility to the long-term effects of different maternal environment. Offspring of genetically identical F1 hybrid dams produced by reciprocal breeding of C57BL/6 and BALB/c parents show alterations in anxiety-related behavior as a consequence of their different maternal environment. Introduction of targeted mutations into these offspring via the father allows for the identification of candidate genes that alter these maternal effects. Our strategy offers several advantages over other methods to study maternal effects, including the use of genetically identical parents, the ability to identify both prenatal and postnatal effects, the straightforward introduction of mutations and its adaptability to high-throughput screening. In order to test the utility of this paradigm to screen candidate genes, we tested for gene-environment interactions involving loss-of-function mutations in the serotonin 1A receptor gene. Our studies demonstrate that early gene-environment interactions can be successfully tested in the mouse. When combined with conditional gene targeting and other molecular genetic techniques available in the mouse, this approach has the potential to identify the molecular mechanisms underlying early gene-environment effects.     

Dynamic interactions between transposable elements and their hosts

Transposable elements (TEs) have a unique ability to mobilize to new genomic locations, and the major advance of second-generation DNA sequencing has provided insights into the dynamic relationship between TEs and their hosts. It now is clear that TEs have adopted diverse strategies - such as specific integration sites or patterns of activity - to thrive in host environments that are replete with mechanisms, such as small RNAs or epigenetic marks, that combat TE amplification. Emerging evidence suggests that TE mobilization might sometimes benefit host genomes by enhancing genetic diversity, although TEs are also implicated in diseases such as cancer. Here, we discuss recent findings about how, where and when TEs insert in diverse organisms.     

The relationship between quaternary structure and enzyme activity

Methods have been developed to study the influence of quaternary structure on enzyme activity. Some enzymes which normally exist as stable oligomers remain catalytically active when the subunits are dissociated by artificial means.     

红壤酶活性与肥力的关系

对供试红壤的基本化学性质、微生物量以及酶活性进行分析.结果表明,红壤脲酶、蔗糖酶、磷酸酶及过氧化氢酶与土壤有机碳、全氮及全磷显著相关或极显著相关,这些酶活性反映了红壤肥力水平的差异.土壤酶活性聚类分析结果与根据土壤化学、生物学性质所得结果基本相似.酶活性可用于评价红壤肥力质量.新鲜土样的酶活性不仅高于风干土样,且与土壤肥力质量联系更为密切.     

The molecular mechanisms of interactions between bioactive peptides and angiotensin-converting enzyme

The ability of milk protein derived Ile-Pro-Ala (IPA), Phe-Pro (FP) and Gly-Lys-Pro (GKP) peptides to inhibit angiotensin I-converting enzyme (ACE), a protein with an important role in blood-pressure regulation, were verified in vitro and in vivo. This work elucidates the modes and molecular mechanisms of the interaction of IPA, FP and GKP with ACE, including mechanisms that bind the peptides to the cofactor Zn²⁺. It was observed that the best docking poses obtained for IPA, FP and GKP were at the ACE catalytic site with very similar modes of interaction, including the interaction with Zn²⁺. The interactions, including H-bonds, hydrophobic, hydrophilic, and electrostatic interactions, as well as the interaction with Zn²⁺, were responsible for the binding between the bioactive peptides and ACE.     

Protein phosphorylation in amyloplasts regulates starch branching enzyme activity and protein-protein interactions

Protein phosphorylation in amyloplasts and chloroplasts of Triticum aestivum (wheat) was investigated after the incubation of intact plastids with gamma-(32)P-ATP. Among the soluble phosphoproteins detected in plastids, three forms of starch branching enzyme (SBE) were phosphorylated in amyloplasts (SBEI, SBEIIa, and SBEIIb), and both forms of SBE in chloroplasts (SBEI and SBEIIa) were shown to be phosphorylated after sequencing of the immunoprecipitated (32)P-labeled phosphoproteins using quadrupole-orthogonal acceleration time of flight mass spectrometry. Phosphoamino acid analysis of the phosphorylated SBE forms indicated that the proteins are all phosphorylated on Ser residues. Analysis of starch granule-associated phosphoproteins after incubation of intact amyloplasts with gamma-(32)P-ATP indicated that the granule-associated forms of SBEII and two granule-associated forms of starch synthase (SS) are phosphorylated, including SSIIa. Measurement of SBE activity in amyloplasts and chloroplasts showed that phosphorylation activated SBEIIa (and SBEIIb in amyloplasts), whereas dephosphorylation using alkaline phosphatase reduced the catalytic activity of both enzymes. Phosphorylation and dephosphorylation had no effect on the measurable activity of SBEI in amyloplasts and chloroplasts, and the activities of both granule-bound forms of SBEII in amyloplasts were unaffected by dephosphorylation. Immunoprecipitation experiments using peptide-specific anti-SBE antibodies showed that SBEIIb and starch phosphorylase each coimmunoprecipitated with SBEI in a phosphorylation-dependent manner, suggesting that these enzymes may form protein complexes within the amyloplast in vivo. Conversely, dephosphorylation of immunoprecipitated protein complex led to its disassembly. This article reports direct evidence that enzymes of starch metabolism (amylopectin synthesis) are regulated by protein phosphorylation and indicate a wider role for protein phosphorylation and protein-protein interactions in the control of starch anabolism and catabolism.     

Ecological lever and interface ecology: epibiosis modulates the interactions between host and environment

The properties of the body surface play a crucial role in most interactions of marine organisms. Critical ecological properties such as drag, morphology, uptake and release of radiation and organic matter are linked to the body surface of an aquatic organism. The properties and functions of this interface may be modified substantially by the presence and activities of epibiotic communities. This, in turn, may lead to substantial modulation of the interactions between the organism bearing epiphytes and its environment, with consequences for the relative fitness of the host organism (basibiont) and its interactors, and ultimately, the structure and functioning of the assemblage. Epibiosis may act as an ecological lever via these indirect effects, greatly amplifying or buffering biotic and abiotic stress.     

Ecological lever and interface ecology: epibiosis modulates the interactions between host and environment

The properties of the body surface play a crucial role in most interactions of marine organisms. Critical ecological properties such as drag, morphology, uptake and release of radiation and organic matter are linked to the body surface of an aquatic organism. The properties and functions of this interface may be modified substantially by the presence and activities of epibiotic communities. This, in turn, may lead to substantial modulation of the interactions between the organism bearing epiphytes and its environment, with consequences for the relative fitness of the host organism (basibiont) and its interactors, and ultimately, the structure and functioning of the assemblage. Epibiosis may act as an ecological lever via these indirect effects, greatly amplifying or buffering biotic and abiotic stress.     

Feedback interactions between needle litter decomposition and rhizosphere activity

The aim of our study was to identify interactions between the decomposition of aboveground litter and rhizosphere activity. The experimental approach combined the placement of labelled litter (¹³C=–37.9) with forest girdling in a 35-year-old Norway spruce stand, resulting in four different treatment combinations: GL (girdled, litter), GNL (girdled, no litter), NGL (not girdled, litter), and NGNL (not girdled, no litter). Monthly sampling of soil CO₂ efflux and ¹³C of soil respired CO₂ between May and October 2002 allowed the partitioning of the flux into that derived from the labelled litter, and that derived from native soil organic matter and roots. The effect of forest girdling on soil CO₂ efflux was detectable from June (girdling took place in April), and resulted in GNL fluxes to be about 50% of NGNL fluxes by late August. The presence of litter resulted in significantly increased fluxes for the first 2 months of the experiment, with significantly greater litter derived fluxes from non-girdled plots and a significant interaction between girdling and litter treatments over the same period. For NGL collars, the additional efflux was found to originate only in part from litter decomposition, but also from the decay of native soil organic matter. In GL collars, this priming effect was not significant, indicating an active role of the rhizosphere in soil priming. The results therefore indicate mutual positive feedbacks between litter decomposition and rhizosphere activity. Soil biological analysis (microbial and fungal biomass) of the organic layers indicated greatest activity below NGL collars, and we suppose that this increase indicates the mechanism of mutual positive feedback between rhizosphere activity and litter decomposition. However, elimination of fresh C input from both above- and belowground (GNL) also resulted in greater fungal abundance than for the NGNL treatment, indicating likely changes in fungal community structure (i.e. a shift from symbiotic to saprotrophic species abundance).     

Modulation of dolichyl-phosphomannose synthase activity by changes in the lipid environment of the enzyme

Rat liver dolichyl-phosphomannose synthase (GDP mannose-dolicholphosphate mannosyltransferase; EC 2.4.1.83) was previously shown to catalyze optimal rates of mannosyl transfer to dolichyl-P when the polyprenol acceptor was incorporated into a phosphatidylethanolamine (PE) matrix that has a tendency to adopt a nonbilayer (hexagonal HII) phase [Jensen, J. W., & Schutzbach, J. S. (1985) Eur. J. Biochem. 153, 41-48]. The present investigations now further define the properties of the lipid environment that are essential for mannosyltransferase activity. Monogalactosyl diglyceride (MGDG), a glycoglycerolipid that prefers a nonbilayer-phase organization in isolation, was shown to provide a suitable lipid matrix for synthase activity. By comparison, the enzyme was not activated by digalactosyl diglyceride (DGDG), which forms stable bilayer structures upon hydration. Enzyme activity in MGDG/DGDG mixtures decreased as the proportion of DGDG in the dispersion was increased. Although bilayer-forming phospholipids supported low rates of mannosyl transfer, enzyme activity was stimulated by the addition of MGDG to either phosphatidylcholine (PC) or PE/PC (1:1) membranes. The incorporation of agents known to destabilize bilayer structures including dolichols, ubiquinone, dodecane, and cholesterol into PE/PC (1:1) membranes also increased the rate of mannosyl transfer. Enzyme activity in PC membranes was stimulated by the presence of gramicidin and also by greatly increased concentrations of the substrate, dolichyl-P. The results demonstrate that the enzyme does not have a requirement for PE and suggest that the physical state of the lipid matrix is an important determinant for reconstitution of the synthase and polyprenol phosphate substrate in a productive complex. The formation of an enzyme/lipid complex was demonstrated by sucrose density gradient centrifugation and could be correlated with the lipid requirements for enzyme activity.     

Subunit interactions in enzyme transition states--antagonism between substrate binding and reaction rate

The principles of structural kinetics as applied to polymeric enzymes have been reinvestigated in order to take account of the probable existence of subunit interactions in the enzyme transition states. On the basis of simple and plausible postulates, structural rate equations have been derived for dimeric enzymes and compared to substrate binding isotherms. It then becomes possible to understand how subunit interactions affect substrate affinity and enzyme reaction rate. There exists an antagonism between substrate binding to the enzyme and the steady state rate of product appearance. If subunit interactions increase the rate of product appearance, they decrease the fractional saturation of the enzyme by the substrate. Alternatively, if they decrease the reaction velocity they increase the fractional saturation. This seemingly paradoxical effect is the direct consequence of subunit interactions occurring in both the ground and the transition states.     

Dynamic morphology of calcium-induced interactions between phosphatidylserine vesicles.

Structural changes in phosphatidylserine vesicles exposed to calcium chloride for various times have been observed by means of video-enhanced light microscopy and freeze-fracture electron microscopy. Large flat double-bilayer diaphragms form at the contacts between aggregated vesicles within milliseconds. Bilayers at and outside of diaphragms rupture and allow vesicles to collapse completely by flattening against each other within seconds. Collapse through intermediate states to a stable multilamellar phase is complete within minutes. The Ca-induced attraction energy and the resultant flattening at contacts between vesicles is far beyond that needed to stress bilayers to the point of rupture. Although the destabilizing response to this stress is preferential to the diaphragm region, 40% of adhering pairs rupture outside of the diaphragm region rather than fuse with each other. In this respect the mechanism of fusion between these vesicles may be fundamentally different from the controlled fusion process in cells.     

Dynamic interactions between limb segments during planar arm movement

Movement of multiple segment limbs requires generation of appropriate joint torques which include terms arising from dynamic interactions among the moving segments as well as from such external forces as gravity. The interaction torques, arising from inertial, centripetal, and Coriolis forces, are not present for single joint movements. The significance of the individual interaction forces during reaching movements in a horizontal plane involving only the shoulder and elbow joints has been assessed for different movement paths and movement speeds. Trajectory formation strategies which simplify the dynamics computation are presented.     

RBSim 2: simulating the complex interactions between human movement and the outdoor recreation environment

This paper describes advancements in recreation management using new technology that couples Geographic Information Systems (GIS) with Intelligent Agents to simulate recreation behaviour in real world settings. RBSim 2 (Recreation Behaviour Simulator) is a computer simulation program that enables recreation managers to explore the consequences of change to any one or more variables so that the goal of accommodating increasing visitor use is achieved while maintaining the quality of visitor experience. RBSim provides both a qualitative understanding of management scenarios by the use of map graphics from a GIS as well as a quantitative understanding of management consequences by generating statistics during the simulation. Managers are able to identify points of over crowding, bottlenecks in circulation systems, and conflicts between different user groups.

RBSim 2 is a tool designed specifically for the purposes of simulating human recreation behaviour in outdoor environments. The software is designed to allow recreation researchers and managers to simulate any recreation environment where visitors are restricted to movement on a network (roads, trails, rivers, etc.). The software architecture is comprised of the following components:

• GIS module to enter travel network, facilities, and elevation data

• Agent module to specify tourist personality types, travel modes, and agent rules

• Typical Trip planner to specify trips as an aggregation of entry/exit nodes, arrival curves, destinations and agents.

• Scenario designer to specify combinations of travel networks, and typical trip plans.

• Statistical module to specify outputs and summarise simulation results

This paper describes the RBSim software architecture with specific reference to the trip planning algorithms used by the recreation agents. An application of the simulator at Port Campbell National Park, Victoria Australia is described.     

Dynamic interactions between cells and their extracellular matrix mediate embryonic development

Cells and their surrounding extracellular matrix microenvironment interact throughout all stages of life. Understanding the continuously changing scope of cell‐matrix interactions in vivo is crucial to garner insights into both congenital birth defects and disease progression. A current challenge in the field of developmental biology is to adapt in vitro tools and rapidly evolving imaging technology to study cell‐matrix interactions in a complex 4‐D environment. In this review, we highlight the dynamic modulation of cell‐matrix interactions during development. We propose that individual cell‐matrix adhesion proteins are best considered as complex proteins that can play multiple, often seemingly contradictory roles, depending upon the context of the microenvironment. In addition, cell‐matrix proteins can also exert different short versus long term effects. It is thus important to consider cell behavior in light of the microenvironment because of the constant and dynamic reciprocal interactions occurring between them. Finally, we suggest that analysis of cell‐matrix interactions at multiple levels (molecules, cells, tissues) in vivo is critical for an integrated understanding because different information can be acquired from all size scales. Mol. Reprod. Dev. 77: 475–488, 2010. © 2010 Wiley‐Liss, Inc.