Octadecyl silica: a solid phase for protein purification by immunoadsorption

Functional conservation between yeast and plant endosomal Na(+)/H(+) antiporters

Vacuolar compartmentation of Na(+) is an essential mechanism for salinity tolerance since it lowers cytosolic Na(+) levels while contributing to osmotic adjustment for cell turgor and expansion. The AtNHX1 protein of Arabidopsis thaliana substituted functionally for ScNHX1, the endosomal Na(+)/H(+) antiporter of yeast. Ion tolerance conferred by AtNHX1 and ScNHX1 correlated with ion uptake into an intracellular pool that was energetically dependent on the vacuolar (H(+))ATPase. AtNHX1 localized to vacuolar membrane fractions of yeast. Hence, both transporters share an evolutionarily conserved function in Na(+) compartmentation. AtNHX1 mRNA levels were upregulated by ABA and NaCl treatment in leaf but not in root tissue.

Identification and characterization of a new porin gene of Klebsiella pneumoniae: its role in beta-lactam antibiotic resistance

Klebsiella pneumoniae porin genes were analyzed to detect mutations accounting for the porin deficiency observed in many beta-lactam-resistant strains. PCR and Southern blot analysis revealed the existence of a third porin gene in addition to the OmpK36 and OmpK35 porin genes previously described. This new porin gene was designated ompK37 and is present in all of the clinical isolates tested. The OmpK37 porin gene was cloned, sequenced, and overexpressed in Escherichia coli. In contrast to that of the major porins, OmpK37 porin expression was only detectable by Western blot analysis in porin-deficient beta-lactam-resistant strains, suggesting strong down regulation under standard laboratory conditions. Functional characterization suggested a narrower pore for the OmpK37 porin than for K. pneumoniae porins OmpK36 and OmpK35. This correlated with the susceptibility to certain beta-lactam antibiotics, since a K. pneumoniae strain expressing porin OmpK37, but not porin OmpK36 or OmpK35, was less susceptible to beta-lactam antibiotics than the same strain expressing either porin OmpK36 or OmpK35.

Functional expression of the ENA1(PMR2)-ATPase of Saccharomyces cerevisiae in Schizosaccharomyces pombe

Na+ efflux and Na+ tolerance depend on a putative P-type ATPase encoded by the gene ENA1(PMR2) in Saccharomyces cerevisiae and on a putative Na+/H+ antiporter encoded by the gene sod2 in Schizosaccharomyces pombe. This report shows that a sod2::ura4 mutant of S. pombe transformed with the ENA1 gene of S. cerevisiae expressed the ENA1 protein, and recovered Na+ efflux and Na+ tolerance. The efflux of Na+ in the wild strain of S. pombe was sensitive to the transmembrane Na+ and H+ gradients, whereas in the sod2::ura4 mutant transformed with ENA1 it was independent of these gradients. The data give further support to the notion that ENA1 and sod2 encode Na+ transporters and not regulators of the process of Na+ export; they show also the physiological consequences of exporting Na+ through an Na(+)-ATPase or an Na+/H+ antiporter.

A simple method for negative and positive selection of murine and human IgM-bearing lymphocytes based on the use of antibody-coated silica microparticles

The use of octadecyl silica microparticles is proposed as an alternative method for negative and positive selection of IgM-bearing lymphocytes. SiC18 microparticles coated with affinity purified IgG anti-IgM were evaluated in their efficiency to deplete IgM-bearing cells. 6 mg of SiC18-IgG depleted an average of 97% IgM-bearing cells from a murine spleen cell suspension and of 84% IgM-bearing cells from human spleen cells. The viability of the selected cells was not affected by this procedure. We also analyzed the ability of whole serum to release IgM-bearing cells from the complex SiC18-target cell. The IgM releasing efficiency was 98%, with a resulting viability of 85%. These results indicate that SiC18 microparticles, saturated with specific antibodies, may be used as an alternative method for depletion or purification of cells bearing the corresponding antigen, from complex cell suspensions. The method is simple, efficient and inexpensive, representing an interesting alternative to the immunomagnetic selection.