Solubility and diffusion of nitrogen in maltodextrin/protein tablets

The gas transport properties of compacted tablets consisting of an amorphous mixture of maltodextrin and sodium caseinate were studied by dissolving nitrogen gas in the tablets and then determining the gas release over time as a function of temperature and water activity. Gas was dissolved in the tablet matrix by heating the tablets under pressure, generally to temperatures above the glass transition temperature of the matrix, holding them at these conditions for a specified time and then rapidly cooling them while maintaining the external pressure. The solubility of nitrogen was found to be largely determined by the free volume of the matrix, which in turn can be influenced to some degree by thermal and pressure treatments during gas loading. At the levels of free volume studied, the dissolved nitrogen is densely packed in the free volume, the packing density being virtually independent of the externally applied pressure. Release of gas from the tablets at temperatures below the glass transition temperature is generally well described by Fickian diffusion. The effective diffusion coefficient of gas release is strongly dependent on the microstructure and porosity of the tablet matrix, and an approximate model describing the relationship between tablet structure and rate of gas release is formulated. The model is in semiquantitative agreement with the rates of gas diffusion obtained for tablets and dense granules. Owing to the structural heterogeneity and variability of the tablets and the history-dependent properties of the tablet matrix, the effective diffusion coefficients of gas release from the tablets showed a relatively large spread. The temperature dependence of diffusional release follows an Arrhenius relation below the glass transition temperature. This allows the prediction of the nitrogen retention in the tablets as function of time, temperature and pressure.     

Human erythroid cells produced ex vivo at large scale differentiate into red blood cells in vivo

New sources of red blood cells (RBCs) would improve the transfusion capacity of blood centers. Our objective was to generate cells for transfusion by inducing a massive proliferation of hematopoietic stem and progenitor cells, followed by terminal erythroid differentiation. We describe here a procedure for amplifying hematopoietic stem cells (HSCs) from human cord blood (CB) by the sequential application of specific combinations of growth factors in a serum-free culture medium. The procedure allowed the ex vivo expansion of CD34+ progenitor and stem cells into a pure erythroid precursor population. When injected into nonobese diabetic, severe combined immunodeficient (NOD/SCID) mice, the erythroid cells were capable of proliferation and terminal differentiation into mature enucleated RBCs. The approach may eventually be useful in clinical transfusion applications.     

Synthesis, and functional properties of a modified human insulin A-chain: implication in a 'mini-insulin' structure determination

The design and total synthesis of a novel insulin A-chain mutant, analogue 3, is reported. In this compound, the cysteines implied in the two insulin inter-chain disulfide bridges are replaced by two serines (residues Ser(A7) and Ser(A20)) and the intra-A-chain disulfide bridge (residues Cys(A6) and Cys(A11)) is conserved. This A-chain analogue (3) has been tested in three in vitro cell culture assays, using insulin as a reference. The data clearly showed that analogue 3 mimics insulin effects on DNA synthesis, glucose uptake and glycogen synthesis without loss of potency as compared to insulin. To our knowledge, these are the first results showing that an isolated insulin chain displays functional properties similar to those of insulin. The implication of these new findings in insulin structure-function relationships and in a 'mini-insulin' structure determination is discussed.     

Reprogramming of the activity of the activator/dissociation transposon family during plant regeneration in rice

Many aspects of epigenetic phenomena have been elucidated via studies of transposable elements. An active transposable element frequently loses its ability to mobilize and goes into an inactive state during development. In this study, we describe the cyclic activity of a maize transposable element dissociation (Ds) in rice. In rice genome, Ds undergoes the spontaneous loss of mobility. However, an inactive state of Ds can be changed into an active state during tissue culture. The recovery of mobility accompanies not only changes in the methylation patterns of the terminal region of Ds, but also alteration in the steady state level of the activator (Ac) mRNA that is expressed by a constitutive CaMV 35S promoter. Furthermore, the Ds-reactivation process is not random, but stage-specific during plantlet regeneration. Our findings have expanded previous observations on Ac reactivation in the tissue culture of maize.     

What are the signaling pathways used by norepinephrine to contract the artery? A demonstration using guinea pig aortic ring segments

The laboratory exercise described in this article used a simple preparation and a straightforward protocol to illustrate how the neurotransmitter norepinephrine (NE) induces an increase of tension in an artery. This was a practical class designed for undergraduate students of the University of Tours. The students performed several protocols to understand how NE acts to contract aortic ring vessels, which sources of calcium are mobilized, and whether the calcium sensitivity of the contractile regulatory apparatus is involved. The design of this exercise allowed students to participate actively in an exercise demonstrating that many mechanisms are involved and act additively to allow arterial tone to develop. Furthermore, the students were introduced to an isolated organ chamber technique that is used to study cellular mechanisms of many tissues and that is still important for smooth muscle research.     

Development of 47 new microsatellite markers from a BTA6 library

Chromosome-specific libraries provide a means to isolate genetic markers from specific chromosomal regions. A small-insert BTA6 library, constructed by microdissection, was screened for dinucleotide repeats (CA)15 and (GA)15. A total of 47 new microsatellite loci were developed and tested for polymorphism and informativeness using the MARC bovine mapping family.     

Three-dimensional structure of manganese superoxide dismutase from Bacillus halodenitrificans,a component of the so-called "green protein"

A so-called "green protein" has been purified from a moderate halophilic eubacterium, Bacillus halodenitrificans (ATCC 49067), under anaerobic conditions. The protein, which might play an important role in denitrification, dissociates mainly into two components after exposure to air: a manganese superoxide dismutase (GP-MnSOD) and a nucleoside diphosphate kinase. As a first step in elucidating the overall structure of the green protein and the role of each component, the 2.8-A resolution crystal structure of GP-MnSOD was determined. Compared with other manganese dismutases, GP-MnSOD shows two significant characteristics. The first is that the entrance to its substrate channel has an additional basic residue-Lys38. The second is that its surface is decorated with an excess of acidic over basic residues. All these structural features may be related to GP-MnSOD's high catalytic activity and its endurance against the special cytoplasm of B. halodenitrificans. The structure of GP-MnSOD provides the basis for recognizing its possible role and assembly state in the green protein.     

Molecular phylogenies support multiple morphological reductions in the liverwort subclass Marchantiidae (Bryophyta)

The phylogeny of one of the putative basal-most group of land plants, the Marchantiidae, is estimated with morphological characters and with sequences of the nuclear (LSU) rDNA gene (first four domains of the 5' end of the 26S rRNA and four subsequent regions) from 34 species and 27 genera. Molecular and morphological data display high degrees of incongruence. The molecular tree topology predominates in the combined analysis. A trend from complex towards simpler morphological traits is apparent from the molecular and combined trees, whereas a trend from simple towards complex traits prevails in the morphological tree. Previously published molecular data corroborate the molecular results. It is suggested that the incongruence stems from the presence of coherent sets of reduction-related morphological traits varying in concert in the morphological data. Marchantiidae is traditionally subdivided into Marchantiales, Sphaerocarpales and Monocleales, with the majority of taxa referred to the first group. The molecular and the combined data both indicate unequivocally that Sphaerocarpales and Monocleales are nested within Marchantiales, and this result is not explicitly refuted by the morphological data.     

A model for regulation of ColE1-like plasmid replication by uncharged tRNAs in amino acid-starved Escherichia coli cells

It has been previously observed that various ColE1-like plasmids replicate differentially in Escherichia coli cells during the relaxed response to amino acid starvation. Here we develop a kinetic model to explain these observations based on the possibility of interaction of the 3' CCA-OH sequence with the UGG triplets in loops of RNA I and RNA II encoded by ColE1-like plasmids. According to our model, when the interaction of uncharged CCA with RNA I is possible, the replication of the ColE1-like plasmid is affected by differences in the concentration of various tRNAs in the starved cell, but it is not affected by the tRNA concentration if the hypothetical pairing occurs between the CCA-OH and RNA II. Using the previously determined parameters for the pBR322 plasmid, the concentration of uncharged tRNAs in the amino acid starved relaxed strains and the assumed efficiency of binding of tRNA and RNA I, we show that our model explains the differences in pBR322 copy number in the relaxed strain starved for several amino acids.     

Structure and phylogeny of the crustacean hyperglycemic hormone and its precursor from a hydrothermal vent crustacean: the crab Bythograea thermydron

The structure of a well-known neurohormone involved in homeostasis regulation and stress response, the crustacean hyperglycemic hormone, was investigated in the deep-sea hydrothermal vent crab Bythograea thermydron. The neuropeptide was isolated from neurohemal organs (sinus glands) and its biological activity checked using an homologous bioassay. Partial amino acid sequence was established by a combination of Edman chemistry and mass spectrometry. Then, the sequence of the cDNA encoding the hormone precursor was determined. The preprohormone is composed of a 29 amino acid signal peptide, followed by a 41 amino acid associated peptide flanking the 72 amino acid hyperglycemic hormone. Comparison of these data with other known crab hyperglycemic hormone and prohormone sequences was performed using phylogenetic analysis methods.