Synthetic approaches to 6-substituted 9-(3-azido-3,4-dideoxy-β-d,l-erythro-pentopyranosyl)purines

Methyl 3-azido-2-O-benzoyl-3,4-dideoxy-β-dl-erythro-pentopyranoside (6) was synthesized through two routes in five steps from methyl 2,3-anhydro-4-deoxy-β-dl-erythro-pentopyranoside (1). The first route proceeded via selective azide displacement of the 3-tosyloxy group of methyl 4-deoxy-2,3-di-O-tosyl-α-dl-threo-pentopyranoside, followed by detosylation and benzoylation. The second route consisted, with a better overall yield, in the azide displacement of the mesyloxy group of methyl O-benzoyl-4-deoxy-3-O-methylsulfonyl-α-dl-threo-pentopyranoside (10), obtained by benzylate opening of 1, followed by benzoylation, debenzylation, and mesylation. Compound 6 was transformed into its glycosyl chloride, further treated by 6-chloropurine to give the nucleoside 9-(3-azido-2-O-benzoyl-3,4-dideoxy-β-dl-erythro-pentopyranosyl)-6-chloropurine (13). When treated with propanolic ammonia, 13 yielded 9-(3-azido-3,4-dideoxy-β-dl-erythro-pentopyranosyl)adenine.     

Homologies between paraflagellar rod proteins from trypanosomes and euglenoids revealed by a monoclonal antibody

A Nonidet P 40 insoluble fraction was isolated from Trypanosoma brucei and was used to raise a monoclonal antibody (5E9). The antigen was localized by indirect immunofluorescence in the flagellum of T. brucei and of two species of euglenoids, Euglena gracilis and Distigma proteus. In immunoblot analysis, 5E9 appeared to bind to paraflagellar rod proteins PFR1 and PFR2 of T. brucei (72000 and 75000 mol. wt.) and of E. gracilis (67000 and 76000 mol. wt.). The presence of a common epitope in paraflagellar rod proteins from species of trypanosomes and euglenoids shows that despite distinct structures of the rods some identical domain exists in the proteins that could be involved in their supramolecular assembly into a similar organelle. The antigenic determinant defined by 5E9 was also shown to be present in a 87000 molecular weight polypeptide located in the proximal part of the flagellum of Crithidia oncopelti in which a paraflagellar rod is not detectable at the ultrastructural level.     

The relationship of hormone-sensitive and hormone-insensitive phosphatidylinositol to phosphatidylinositol 4,5-bisphosphate in the WRK-1 cell

We have previously characterized two distinct pools of phosphatidylinositol (PI) in the WRK-1 rat mammary tumor cell, one whose metabolism is enhanced in response to vasopressin and another which is insensitive to hormonal manipulation. The purpose of the present study was to examine the relationship between cellular phosphatidylinositol 4,5-bisphosphate (PIP2) and each of the two PI pools. We have found that in WRK-1 cells, vasopressin induces the rapid loss of PIP2 and the accumulation of inositol phosphates. By making use of kinetic differences in 32Pi uptake into the two pools of PI and assessing radioactivity levels in the 1-phosphate of PIP2, we have determined that hormone-sensitive PI is the precursor of approximately 60% of the cellular PIP2; the remainder is synthesized from the hormone-insensitive pool. Additional data indicate that PIP2 derived from hormone-sensitive PI is likewise hormone-sensitive, while that synthesized from hormone-insensitive PI remains stable over a long period of time and is not affected by the presence of vasopressin.     

A fluorescence study of the binding of cytochrome C to mixed-phospholipid microvesicles : evidence for a preferred orientation of the bound protein.

Kinetic and equilibrium experiments are reported on the binding of the fluorescent probe 1,8-anilino-naphtalene sulfonate (ANS) to microvesicles of natural lecithin containing 10 per cent of an anionic phospholipip (90 : 10 mixtures). Kinetics discriminated between fast binding to the outer leaflet of the bilayer and apparently slow binding to the inner leaflet controlled by the diffusion of the probe across the bilayer. The equilibrium distribution of ANS between the two leaflets was not dependent on the nature of the anionic species and the spectral properties of bound ANS were identical in all cases investigated. A hyperbolic saturation was observed allowing to propose an affinity scale for the binding of ANS to mixtures of lecithin with phosphatidic acid, phosphatidylinositol, and cardiolipin. The effects on binding of ionic strength and sodium dodecylsulfate were also considered. The binding of horse heart ferricytochrome c to ANS-labelled microvesicles was studied quantitatively making use of the quenching of the probes fluorescence by the heme. Perrin-F?rster energy transfer could be analysed on the basis of a simple model of the physical arrangement of the system which was elaborated from published data referring to ANS and cytochrome c binding to phospholipids. Experimental and theoretical computed values of the quenching efficiency were compared and led to conclude in favor of a preferred orientation of the heme crevice fully accessible from the external space at the lipid interface.     

Potentiation of the antagonistic effect of ACTH11-24 on steroidogenesis by synthesis of covalent dimeric conjugates

Covalent dimerization of the adrenocorticotropin fragment ACTH11-24 increases its antagonistic potency on the ACTH-induced steroidogenesis in isolated bovine fasciculata/reticularis cells by 3 orders of magnitude when the C-termini are linked via a 10 A long spacer. This strong potentiation, probably mediated by cross-linking of the receptors, was shown to be dependent on the point of attachment of the monomeric fragment to the spacer, thus providing information about the position of the binding site in the hormonal segment and about the distance of the receptors on the cell surface.