Abstract Four classes of 6-X-benzylated purine nucleosides, (i) 6-N-(substituted-benzyl)adenosines, (ii) 6-N-(4-nitrobenzyl)adenine nucleosides with modified sugars, (iii) 6-N(S)-(4-azidobenzyl) derivatives of adenosine, 6-thioinosine, and 6-thioguanosine, and (iv) 6-N-{4-N-[acyl(sulfonyl)amino]benzyl}adenosines, were synthesized and their binding interactions with “es-NT” ( e quilibrative, inhibitor-sensitive nucleoside transport) systems were studied. Several tight-binding analogues were found.
A considerable increase in several heat shock proteins (HSPs) amount in Acholeplasma laidlawii cells has been revealed after temperature rising of liquid culture; and the quantity of small HSP, named p17, was increased in a hundred of times. The p17 protein was isolated and identified as HSP of alpha-crystallin type (alpha-HSP). It became possible as a result of sequencing of 15 amino acids from N-terminal of the p17 polypeptide chain, followed by revealing of a corresponding open reading frame (ORF) in a completely sequenced genome of A. laidlawii PG 8A. Computer-based search for homologous ORFs in all 17 genomes of Mycoplasmataceae family (the mycoplasmas themselves) that had been completely sequenced to date, gives negative result. But among the representatives of Mollicutes (mycoplasma) class, the genes coding alpha-HSPs were found in two Phytoplasma species (Phytoplasmataceae family) and the acholeplasma examined (Acholeplasmataceae family). It supposed that presence or absence of alpha-HSPs in microorganisms might be connected with the fact that representatives of Acholeplasmataceae and Phytoplasmataceae families inhabit principally in plant tissues in contrast to majority of Mycoplasmataceae family, that inhabit animal and human tissues, i. e. use ecological niches with relatively constant temperature.
Site-specific binding of nitrobenzylthioinosine (NBMPR) to plasma membranes of some animal cells results in the inhibition of the facilitated diffusion of nucleosides. The present study showed that nucleoside transport in Novikoff UA rat hepatoma cells is insensitive to site-saturating concentrations of NBMPR. Equilibrium binding experiments demonstrated the presence of high-affinity sites for NBMPR in a membrane-enriched fraction from these cells. In the presence of uridine or dipyridamole, specific binding of NBMPR at these sites was inhibited. When Novikoff UA membranes were covalently labelled with [3H]NBMPR by using photoaffinity techniques, specifically bound radioactivity was incorporated exclusively into a polypeptide(s) with an apparent Mr of 72,000-80,000, determined by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. Covalent labelling of this polypeptide was abolished in the presence of excess nitrobenzylthioguanosine (NBTGR) and reduced in the presence of adenosine, uridine or dipyridamole. The apparent Mr of the NBMPR-binding polypeptide in Novikoff UA cells is significantly higher than that reported for corresponding polypeptides in other cell types (Mr 45,000-66,000). When membrane-enriched preparations from S49 mouse lymphoma cells were photolabelled and mixed with labelled NovikoffUA membrane-enriched preparations, gel electrophoresis resolved the NBMPR-binding polypeptides from the two preparations.
The toxicity to mice of combinations of 1-beta-D-arabinofuranosylcytosine and 3-deazauridine was investigated. The drugs were administered daily i.p. on Days 1 to 5, each drug at 10 mg/kg body weight; these dosages are small fractions of the dosages at which 10% of the treated animals died when either drug was administered alone on the foregoing schedule. This drug combination was severely toxic when 3-deazauridine was administered 2 to 8 hr prior to 1-beta-D-arabinofuranosylcytosine; most mice treated in this way died within 3 days of the last treatment. Histological examination showed that severe damage to the small bowel mucosa resulted from treatment with the drugs in the above, lethal sequence. In contrast, treatments with this drug combination at the same dosages were tolerated when the two agents were administered simultaneously or when 1-beta-D-arabinofuranosylcytosine preceded 3-deazauridine. Under the latter conditions, small bowel mucosal injury was much less severe. Female mice were more sensitive to the toxic treatment regimen than were male mice and were protected against the latter when either the 3-deazauridine or the 1-beta-D-arabinofuranosylcytosine component was preceded by treatment with nitrobenzylthioinosine (100 mg/kg), a potent inhibitor of nucleoside transport.
'/%3e%3cuse xlink:href='%23a' transform='rotate(144 450 300)'/%3e%3cuse xlink:href='%23a' transform='rotate(216 450 300)'/%3e%3cuse xlink:href='%23a' transform='rotate(288 450 300)'/%3e%3c/svg%3e)