Chiral synthesis of a dithiolester analog of phosphatidylcholine as a substrate for the assay of phospholipase A2

The synthesis of a dithiolester analog of phosphatidylcholine, 1,2-bis(heptanoylthio)-1,2-dideoxy-sn-glycerol-3-phosphocholine (thio PC), is described. Starting with 1-trityl-sn-glycerol (prepared from D-mannitol), tosylation followed by displacement with potassium methyl xanthate gave a trithiocarbonate. Reductive cleavage of the latter gave a 1,2-dithiol which was then acylated, detritylated, and esterified with choline phosphate. Hydrolysis of thio PC by phospholipase A2 (Naja naja) indicated 95% chiral purity. The rate of hydrolysis as a function of substrate concentration showed a sharp increase at about 0.17 mM, the critical micellar concentration of the lipid. A spectrophotometric assay of phospholipase A2 (by measurement of released thiol groups in the presence of dithionitrobenzoic acid) was quite sensitive. As little as 1 ng of enzyme was detected, representing a rate of about 0.2 nmol of substrate hydrolyzed per min.     

Regulation of a restriction and modification system via DNA inversion in Mycoplasma pulmonis

An invertible DNA element of 6.8 kb, designated the hsd1 locus, was identified in the chromosome of Mycoplasma pulmonis. Infection of host cells with mycoplasma virus P1 revealed that the organism's restriction and modification (R-M) properties are controlled by inversion of hsd1. The nucleotide sequence of hsd1 revealed several genes, the predicted amino acids of which bear striking similarity to the subunits of the type I R-M enzymes previously found only in enteric bacteria.     

Evidence for type III restriction and modification systems in Mycoplasma pulmonis

Mycoplasma pulmonis possesses a cassette of genes that are predicted to code for type III restriction and modification (R-M) enzymes. Transposon disruption of a gene predicted to code for the endonuclease subunit of the enzyme resulted in loss of R-M activity. Genomic data indicate that the cassette was acquired by horizontal gene transfer and possibly located on a mobile element.     

Leaf architecture characters of <i>Vachellia tortilis</i> (Forssk.) Galasso and Banfi along longitudinal gradient in Limpopo Province,South Africa

This paper looked at the leaf architecture characteristics of Vachellia tortilis to determine if either there is or not an effect of the tropic line on plants. Vachellia tortilis leaves were sampled along a national road (N1) in Limpopo province. Sampling points were set 10 km apart away from the Tropic of Capricon in opposite directions. Leaf morphology revealed that leaves of V. tortilis are bipinnately compound with alternate arrangement. The venation pattern of the pinnules was eucamptodromus and brochidodromous with imperfect reticulation. Areoles were imperfect and pentagonal or irregular in shape.     

The vir gene of bacteriophage MAV1 confers resistance to phage infection on Mycoplasma arthritidis

Lysogenization of Mycoplasma arthritidis with the MAV1 bacteriophage increases the virulence of the mycoplasma in rats. The MAV1 vir gene is one of only two constitutively transcribed phage genes in the lysogen. We show here that Vir is a lipoprotein and is located on the outer surface of the cell membrane. To investigate whether Vir is a virulence factor, the vir gene was cloned into the transposon vector Tn4001T and inserted in the genome of the nonlysogen strain 158. The virulence of the resulting transformants was no different from that of the parent strain. Interestingly, all vir-containing transformants were resistant to infection by MAV1. Vir had no effect on MAV1 adsorption. We conclude that Vir is not a virulence factor but functions to exclude superinfecting phage, possibly by blocking the injection of phage DNA into the bacterial cytoplasm.     

The usage of marker traits in plants for evaluation of resistance of the winter wheat to pest insects

A new method of selection of the winter wheat varieties has been tested for resistance to the pest insects' complex by the traits of plants that are the markers of plant resistance. It makes it possible to use this method from year to year independently of the pests' density.     

A corresponding tyrosine residue in the C2/factor B type A domain is a hot spot in the decay acceleration of the complement C3 convertases

The cleavage of C3 by the C3 convertases (C3bBb and C4b2a) determines whether complement activation proceeds. Dissociation (decay acceleration) of these central enzymes by the regulators decay-accelerating factor (DAF), complement receptor 1 (CR1), factor H, and C4-binding protein (C4BP) controls their function. In a previous investigation, we obtained evidence implicating the alpha4/5 region of the type A domain of Bb (especially Tyr338) in decay acceleration of C3bBb and proposed this site as a potential interaction point with DAF and long homologous repeat A of CR1. Because portions of only two DAF complement control protein domains (CCPs), CCP2 and CCP3, are necessary to mediate its decay of the CP C3 convertase (as opposed to portions of at least three CCPs in all other cases, e.g. CCPs 1-3 of CR1), DAF/C4b2a provides the simplest structural model for this reaction. Therefore, we examined the importance of the C2 alpha4/5 site on decay acceleration of C4b2a. Functional C4b2a complexes made with the C2 Y327A mutant, the C2 homolog to factor B Y338A, were highly resistant to DAF, C4BP, and long homologous repeat A of CR1, whereas C2 substitutions in two nearby residues (N324A and L328A) resulted in partial resistance. Our new findings indicate that the alpha4/5 region of C2a is critical to decay acceleration mediated by DAF, C4BP, and CR1 and suggest that decay acceleration of C4b2a and C3bBb requires interaction of the convertase alpha4/5 region with a CCP2/CCP3 site of DAF or structurally homologous sites of CR1 and C4BP.     

Transformation of Mycoplasma pulmonis and Mycoplasma hyorhinis: transposition of Tn916 and formation of cointegrate structures

A procedure for transformation of the murine pathogen Mycoplasma pulmonis with plasmid pAM120 was developed. This plasmid replicates in Escherichia coli and contains the gram-positive transposon Tn916. The transformation protocol also proved effective for the swine pathogen Mycoplasma hyorhinis. The tetracycline resistance determinant of Tn916 was expressed in transformed myocoplasma cells, and Tn916 was found inserted into numerous sites in the recipient chromosomes of M. pulmonis and M. hyorhinis, indicating that transposition had occurred. Interestingly, some transformants of M. pulmonis and M. hyorhinis contained cointegrate structures which apparently had a complete copy of the entire donor plasmid (pAM120) inserted into the recipient chromosome. Subsequent transposition of inserted Tn916 was observed in passaged clones of transformed M. pulmonis.     

Optimized labeling of bone marrow mesenchymal cells with superparamagnetic iron oxide nanoparticles and <Emphasis Type="Italic">in vivo</Emphasis> visualization by magnetic resonance imaging

Background  

Stem cell therapy has emerged as a promising addition to traditional treatments for a number of diseases. However, harnessing the therapeutic potential of stem cells requires an understanding of their fate in vivo. Non-invasive cell tracking can provide knowledge about mechanisms responsible for functional improvement of host tissue. Superparamagnetic iron oxide nanoparticles (SPIONs) have been used to label and visualize various cell types with magnetic resonance imaging (MRI). In this study we performed experiments designed to investigate the biological properties, including proliferation, viability and differentiation capacity of mesenchymal cells (MSCs) labeled with clinically approved SPIONs.