Some characteristics of monolayers of 1-palmitoyl-2-oleoyl-phosphatidylglycerol with and without dipalmitoylphosphatidylcholine during dynamic compression and expansion

Some properties of monolayers of $\text{1-}\text{palmitoyl}\text{-2-}\text{oleoyl}\text{-sn-}\text{glycero}\text{-3-}\text{phospho}\text{-rac-}\text{glycerol}$ (POPG) alone or of POPG in mixtures with $\text{1,2-}\text{dipalmitoyl}\text{-sn-}\text{glycero}\text{-3-}\text{phosphocholine}$ (DPPC) have been measured near 35°C during dynamic compression and expansion at 3.6 cm²·s^?1. (2) The mean values of minimum surface tension (corresponding to maximum surface pressure) which could be obtained with pure POPG monolayers at high compression ranged from 15 to 18 mN·m^?1 in the presence of Na⁺, Ca²⁺ or low pH (2.0) in the subphase. (3) The presence of Ca²⁺ or low pH in the subphase increased the collapse plateau ratios obtained on cyclic compression. This might represent enhanced respreading into the monolayer of pure POPG from a collapsed form during reexpansion of the surface. (4) Monolayers containing 10% or 30% POPG and 90% or 70% DPPC could be compressed to surface tensions approaching zero. (5) In such mixed monolayers, 10% or 30% POPG did not appear to enhance respreading, as measured by collapse plateau ratios, in the presence of Na⁺ or Ca²⁺ in the subphase.     

Interactions of Bax and tBid with Lipid Monolayers

The release of cytochrome c from mitochondria to the cytosol is a crucial step of apoptosis that involves interactions of Bax and tBid proteins with the mitochondrial membrane. We investigated Bax and tBid interactions with (i) phosphatidylcholine (PC) monolayer as the main component of the outer leaflet of the outer membrane, (ii) with phosphatidylethanolamine (PE) and phosphatidylserine (PS) that are present in the inner leaflet and (iii) with a mixed PC/PE/Cardiolipin (CL) monolayer of the contact sites between the outer and inner membranes. These interactions were studied by measuring the increase of the lipidic monolayer surface pressure induced by the proteins. Our measurements suggest that tBid interacts strongly with the POPC/DOPE/CL, whereas Bax interaction with this monolayer is about 12 times weaker. Both tBid and Bax interact moderately half as strongly with negatively charged DOPS and non-lamellar DOPE monolayers. TBid also slightly interacts with DOPC. Our results suggest that tBid but not Bax interacts with the PC-containing outer membrane. Subsequent insertion of these proteins may occur at the PC/PE/CL sites of contact between the outer and inner membranes. It was also shown that Bax and tBid being mixed in solution inhibit their insertion into POPC/DOPE/CL monolayer. The known 3-D structures of Bax and Bid allowed us to propose a structural interpretation of these experimental results.     

A simple model of plankton population dynamics coupled with a LES of the surface mixed layer

The concentration of phytoplankton in the sea is affected by biological processes, such as growth/mortality rates, predatory zooplankton concentrations and nutrient levels. Phytoplankton concentrations are also influenced by physical processes, in particular the mixing properties of the local fluid environment. On planktonic scales (approximately 10-1000 microm) one can assume the local turbulent flow is isotropic, with no distinction between horizontal and vertical mixing. However, agglomerations of phytoplankton into patches are observed on larger scales of up to hundreds of metres, whose formation will be influenced by the anisotropic advection/mixing properties and large-eddy structures prevalent in the surface mixed layer. This paper presents the results of the coupling of a large-eddy simulation (LES) model of the mixed layer with an advection-diffusion system of coupled equations for nitrate-phytoplankton-zooplankton (NPZ) concentration, incorporating sub-grid parameterizations of the biological processes. Typically these include phytoplankton growth due to light levels and ambient nitrate concentration, offset by grazing losses due to the presence of zooplankton. The primary goal of this work is to investigate how the characteristics of the mixed layer turbulence influence the observed distribution of phytoplankton. One novel feature is the incorporation of a 'vortex-force' term in the LES code in order to generate Langmuir circulations. It has been speculated that the enhanced mixing rates associated with 'Langmuir turbulence' play a significant role in regulating planktonic activity. Results derived from the coupled LES-NPZ model, run with and without the presence of Langmuir circulations, are presented in order to investigate these ideas.     

Syntheses and structures of four- and five-coordinate bio-related zinc complexes containing dithiolate-diamine ligands

Two new zinc complexes, namely, [{Zn(N₂H₂S₂)}₂] (3) [N₂H₂S₂²⁻ = N,N-bis(2-mercaptophenyl)ethylendiamine (2−)] and [Zn(N₂Me₂S₂)] (4) [N₂Me₂S₂²⁻ = N,N′-dimethyl-N,N′-bis(2-mercaptophenyl)ethylendiamine) (2−)] have been synthesized and structurally characterized by X-ray structure analyses. The structure of 3 consists of a bis(μ-thiolato) binuclear unit, in which each zinc center was found to reside in an N₂S₃ array between square-pyramidal and trigonal-bipyramidal environment. The two zinc centers are bridged by one of the two thiolates of an [N₂S₂] ligand. In the crystal packing, the neighboring binuclear units interact with each other by H-bonding interaction, which extends the binuclear unit into a 3D network. In contrast to 3 complex 4 is mononuclear, where each zinc center now was found to reside in an N₂S₂ distorted tetrahedral environment with a large S-Zn-S bite angle. The relevance of these compounds in biological systems is discussed. Unlike 3, the formation of hydrogen bridges in 4 is no longer possible and instead the molecular packing is determined by π-stacking between the phenyl rings.     

Intraspecific brood-mixing of the cichlid fishPerissodus microlepis in Lake Tanganyika

Synopsis The frequency and origin of intraspecific brood-mixing in the biparental cichlid fishPerissodus microlepis were investigated by the cohort analysis of schooling young and the underwater observation of guarding parents. The cohort analysis showed that brood-mixing started from the early guarding state when the young were smaller than 10 mm standard length and nearly all schools of young larger than 16 mm contained alien young from up to 6 broods. Brood farming-out of this fish, which was originally proposed to be a way adopted only by a deserted parent, was performed also by paired parents. We suggest that brood-mixing inP. microlepis is attributed mainly to brood farming-out by paired and deserted parents.     

Association between life-span extension by caloric restriction and thiol redox state in two different strains of mice

The hypothesis that the life-extending effect of caloric restriction (CR) is associated with an attenuation of the age-related pro-oxidant shift in the thiol redox state was tested employing a novel experimental design. Amounts of GSH, GSSG, and protein mixed disulfides (Pr-SSG) in the skeletal muscle and liver were compared between two strains of mice that have similar life spans when fed ad libitum (AL), but different life spans under the standard CR regimen. The life span of one strain, C57BL/6, is extended under CR, whereas it remains unaffected in the other strain, DBA/2. Mice were fed AL or 40% less food starting at 4 months and compared at 6 and 24 months of age. The amounts of GSSG and Pr-SSG increased and the GSH:GSSG ratios decreased with age in both strains of AL-fed mice. CR prevented these age-related changes in the C57BL/6, whose life span is extended by CR, but not in the DBA/2 mice, in which it remains unaffected. CR enhanced the activity of glutamate-cysteine ligase in the C57BL/6, but not in the DBA/2 mice. The results suggest that longevity extension by CR may be associated with the attenuation of age-related pro-oxidizing shifts in the thiol redox state.     

Mixed substrate growth of methylotrophic yeasts in chemostat culture: Influence of the dilution rate on the utilisation of a mixture of glucose and methanol

The growth of Hansenula polymorpha and Kloeckera sp. 2201 with a mixture of glucose and methanol (38.8%/61.2%, w/w) and the regulation of the methanol dissimilating enzymes alcohol oxidase, catalase, formaldehyde dehydrogenase and formate dehydrogenase were studied in chemostat culture, as a function of the dilution rate. Both organisms utilized and assimilated glucose and methanol simultaneously up to dilution rates of 0.30 h^-1 (H. polymorpha) and 0.26h^-1, respectively (Kloeckera sp. 2201) which significantly exceeded _max found for the two yeasts with methanol as the only source of carbon. At higher dilution rates methanol utilisation ceased and only glucose was assimilated. Over the whole range of mixed-substrate growth both carbon sources were assimilated with the same efficiency as during growth with glucose or methanol alone.In cultures of H. polymorpha, however, the growth yield for glucose was lowered by the unmetabolized methanol at high dilution rates. During growth on both carbon sources the repression of the synthesis of all catabolic methanol enzymes which is normally caused by glucose was overcome by the inductive effect of the simultaneously fed methanol. In both organisms the synthesis of alcohol oxidase was found to be regulated differently as compared to catalase, formaldehyde and formate dehydrogenase. Whereas increasing repression of the synthesis of alcohol oxidase was found with increasing dilution rates as indicated by gradually decreasing specific activities of this enzyme in cell-free extracts, the specific activities of this enzyme in cell-free extracts, the specific activities of catalase and the dehydrogenases increased with increasing growth rates until repression started. The results indicate similar patterns of the regulation of the synthesis of methanol dissimilating enzymes in different methylotrophic yeasts.Abbreviations and Terms C₁ Methanol - C₆ glucose; D dilution rate (h^-1) - D _c critical dilution rate (h^-1) - q _s specific, rate of substrate consumption (g substrate [g cell dry weight]^-1 h^-1) - q _CO2 and q _O2 are the specific rates of carbon dioxide release and oxygen consumption (mmol [g cell dry weight]^-1 h^-1) - RQ respiration quotient (q _CO2 q _O2 ¹ ) - s ₀(C₁) and s ₀(C₆) are the concentrations of methanol and glucose in the inflowing medium (g l^-1) - s residual substrate concentration in the culture liquid (g l^-1) - Sp. A. enzyme specific activity - x cell dry weight concentration (gl^-1) - Y _X/C6 growth yield on glucose (g cell dry weight [g substrate]^-1     

Ca<Superscript>2+</Superscript> channel currents of cortical neurons from pure and mixed cultures

Voltage-gated Ca²⁺ channels (VGCCs) are key regulators of many neuronal functions, and involved in multiple central nervous system diseases. In the last 30 years, a large number of injury and disease models have been established based on cultured neurons. Culture with serum develops a mixture of neurons and glial cells, while culture without serum develops pure neurons. Both of these neuronal-culture methods are widely used. However, the properties of Ca²⁺ currents in neurons from these two cultures have not been compared. In this study, we cultured rat cortical neurons in serum-containing or -free medium and then recorded the Ca²⁺ channel currents using patch-clamp technique. Our results showed that there were significant differences in the amplitude and activation properties of whole-cell Ca²⁺ channel currents, and of non-L-type Ca²⁺ channel currents between the neurons from these two culture systems. Our data suggested that the difference of whole-cell Ca²⁺ currents may result from the differences in non-L-type currents. Understanding of these properties will considerably advance studies of VGCCs in neurons from pure or mixed culture.     

Competition between wild-type and a marked recombinant baculovirus (Spodoptera exigua nucleopolyhedrovirus) with enhanced speed of action in insect larvae

Competition between virus genotypes in insect hosts is a key element of virus fitness, affecting their long-term persistence in agro-ecosystems. Little information is available on virus competition in insect hosts or during serial passages from one cohort of hosts to the next. Here we report on the competition between two genotypes of Spodoptera exigua nucleopolyhedrovirus (SeMNPV), when serially passaged as mixtures in cohorts of 4th instar S. exigua larvae. One of the genotypes was a SeMNPV wild-type isolate, SeUS1, while the other was a SeMNPV recombinant (SeMNPV-XD1) having a greater speed of kill than SeUS1. SeXD1 lacks a suite of genes, including the ecdysteroid UDP-glucosyl transferase (egt) gene. SeXD1 expresses the green fluorescent protein (GFP) gene, enabling the identification of SeXD1 in cell culture and in insects. The relative proportion of SeUS1 and SeXD1 in successive passages of mixed infections in various ratios was determined by plaque assays of budded virus from infected larvae and by polymerase chain reactions and restriction enzyme analyses. The SeUS1 genotype outcompeted recombinant SeXD1 over successive passages. Depending on the initial virus genotype ratio, the recombinant SeXD1 was no longer detected after 6-12 passages. A mathematical model was developed to characterize the competition dynamics. Overall, the ratio SeUS1/XD1 increased by a factor 1.9 per passage. The findings suggest that under the experimental conditions recombinant SeXD1 is displaced by the wild-type strain SeUS1, but further studies are needed to ascertain that this is also the case when the same baculoviruses would be used in agro-ecosystems.