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751 records · Page 42Linked to original sources
PubMed1982

Transport mechanisms of 6-diazo-5-oxo-L-norleucine in Escherichia coli K-12.

The diazo antibiotic 6 diazo-5-oxo-L-norleucine is transported into Escherichia coli using the general aromatic amino acid transport system and a specific phenylalanine transport system. Resistance to this antibiotic is the result of a decreased rate of transport of the antibiotic and also the result of a more rapid rate of efflux of the antibiotic from the cell.

Amino Acids↗
PubMed1978

Comparison of the effect of drugs on Babesia in vitro and in vivo.

It was previously shown that Babesia-infected blood maintained in vitro incorporated high levels of 3H hypoxanthine and that the uptake could be suppressed by babesicidal drugs. In the current paper the hypoxanthine pathway was shown to be the most sensitive in testing such drugs for activity in vitro. Other pathways involving orotic acid, glutamine or thymidine were less sensitive. The highest counts were achieved when 3H hypoxanthine was added 1 h after cultures were set up. Drugs which had previously shown activity against Babesia in vitro were added to cultures of B rodhaini and after 24 h incubation parasitised cells were inoculated into groups of mice. Known babesicidal drugs suppressed or delayed infection in mice and 3H hypoxanthine analogues also showed some activity. These analogues, however, showed no therapeutic properties when injected into B rodhaini infected mice.

Animals↗
PubMed1996

Coordinated regulation in human T cells of nucleotide-hydrolyzing ecto-enzymatic activities, including CD38 and PC-1. Possible role in the recycling of nicotinamide adenine dinucleotide metabolites.

The human leukocyte surface Ag CD38 was recently identified as a nicotinamide adenine dinucleotide (NAD)(+)-glycohydrolase ecto-enzyme, degrading NAD into nicotinamide and ADP-ribose. We show here that expression of CD38 is increased in the Jurkat T cell line after treatment with agents that augment intracellular cAMP, with the permeant cAMP analogue dibutyryl-cAMP (db-cAMP), and also with PMA, which activates protein kinase C. Treatment of human PBL T cells with db-cAMP or submitogenic doses of PMA also increased CD38 expression. Two other nucleotide-hydrolyzing activities were induced on the T cell surface concomitantly with CD38: the human PC-1 molecule, a nucleotide phosphodiesterase/pyrophosphatase that produces AMP from NAD or ADP-ribose, and a nucleotidase that produces adenosine from AMP, but which may be distinct from the CD73 5'-nucleotidase. All three enzymes were up-regulated after stimulation of human peripheral blood T cells with PHA. The coordinated regulation of these ecto-enzymes suggested that, besides a possible signaling function, they may recycle extracellular NAD by degrading it to adenosine and nicotinamide, which can be taken up by cells. In support of this hypothesis, db-cAMP-treated Jurkat cells could degrade extracellular NAD for de novo synthesis of purines, while untreated cells could not. Activated lymphocytes are often located in tissues in which cell death is common. It is suggested that the coordinated expression of these enzymes may allow activated T cells to re-use NAD and nucleotides from dead cells.

ADP-ribosyl Cyclase↗