Thromboxane receptor antagonism combined with thromboxane synthase inhibition. 6. 4-substituted 3-pyridinylalkanoic acids.

(3-Pyridinyl)alkanoic acids substituted at the 4-position with an (arylsulfonamido)alkyl group were synthesized and found to behave as platelet thromboxane receptor antagonists (TxRAs) and thromboxane synthase inhibitors (TxSIs). The compounds behaved as agonists at the vascular receptor for thromboxane A₂.     

Amino acid analysis utilizing phenylisothiocyanate derivatives

Advances in liquid chromatography have brought about the development of new techniques in amino acid analysis which take full advantage of precolumn derivatization procedures. Using phenylisothiocyanate as the reagent, detection limits under 1 pmol can be routinely achieved, allowing the analysis of submicrogram protein samples. Analysis times as short as 10 min for samples after hydrolysis and 1 h for physiologic samples are possible. Accurate, reproducible quantitation of amino acids can be obtained from complex matrices such as plasma, urine, feed, and food samples. This level of performance and flexibility gives the analyst the first realistic alternative to ion-exchange analysis without compromising desirable features of the traditional methodology.     

Primary structure of the site on bovine hormone-sensitive lipase phosphorylated by cyclic AMP-dependent protein kinase

The primary structure of a region on hormone-sensitive lipase was determined to be: Lys-Thr-Glu-Pro-Met-Arg-Arg-Ser- Val-Ser-Glu-Ala-Ala-Leu-Thr-Gln-Pro-Glu-Gly-Pro-Leu-Gly-Thr-Asp-Ser-Leu-Lys. Ser-8 was the only residue in the intact protein phosphorylated by cyclic AMP-dependent protein kinase. However, Ser-10 also appeared to be present in a phosphorylated form, suggesting that it is a target for a distinct protein kinase in vivo.     

Complete nucleotide sequence of the Streptomyces lividans plasmid pIJ101 and correlation of the sequence with genetic properties.

The complete nucleotide sequence of the multicopy Streptomyces plasmid pIJ101 has been determined and correlated with previously published genetic data. The circular DNA molecule is 8,830 nucleotides in length and has a G+C composition of 72.98%. The use of a computer program, FRAME, enabled identification in the sequence of seven open reading frames, four of which, tra (621 amino acids [aa]), spdA (146 aa), spdB (274 aa), and kilB (177 aa), appear to be genes involved in plasmid transfer. At least two of the above genes are predicted to be transcribed by known promoters that are regulated in trans by the products of the korA (241 aa) and korB (80 aa) loci on the plasmid. The segment of the plasmid capable of autonomous replication contains one large open reading frame (rep; 450 aa) and a noncoding region presumed to be the origin of replication. Four other small (less than 90 aa) open reading frames are also present on the plasmid, although no function can be attributed to them. The sequence of the pIJ101 replication segment present in several widely used cloning vectors (e.g., pIJ350 and pIJ702) has also been determined, so that the complete nucleotide sequences of these vectors are now known.     

Site-directed mutagenesis of the charged residues near the carboxy terminus of the colicin E1 ion channel

Colicin E1 was altered by oligonucleotide-directed mutagenesis at the site of three charged residues on the COOH side of the 35-residue hydrophobic segment in the channel-forming domain. Asp-509 is one of five conserved acidic residues in the channel domain of colicins A, B, E1, Ia, and Ib and is the first charged residue following the hydrophobic segment, followed by the basic residues Lys-510 and Lys-512. Asp-509 and Lys-512 were changed to amber and ochre stop codons, respectively, while Lys-510 was mutated to a Met codon. Proteins truncated after residue 508 or 511, and missing the last 14 or 11 residues, were obtained from a nonsuppressing cell strain harboring the mutant plasmid while full-length colicin molecules with single residue changes at Asp-509 to Leu, Ser, and Gln, and Lys-512 to Tyr, were obtained by using appropriate suppressor strains. The truncated colicins displayed (i) a low cytotoxicity, approximately 1% of intact wild-type colicin, (ii) 10-fold less in vitro channel activity with liposomes, and (iii) reduced labeling of the colicin in liposomes by a phospholipid photoaffinity probe, showing that one or more of the residues following Asn-511 is necessary for both in vivo and in vitro activity and insertion into the bilayer. (iv) The truncated mutants also displayed an altered conformation at pH 6 that allowed greater binding and activity with liposomes at this pH relative to wild type. The cytotoxicity of single residue substitutions at Asp-509 showed a range of cytotoxicities, wild type greater than Ser-509 greater than Gln-509 greater than Leu-509, although none of these changes greatly affected the in vitro channel activity or pH dependence.(ABSTRACT TRUNCATED AT 250 WORDS)     

Photolabeling of membrane-bound Torpedo nicotinic acetylcholine receptor with the hydrophobic probe 3-trifluoromethyl-3-(m-[125I]iodophenyl)diazirine

The hydrophobic, photoactivatable probe 3-trifluoromethyl-3-(m-[125I]iodophenyl)diazirine ([125I]TID) was used to label acetylcholine receptor rich membranes purified from Torpedo californica electric organ. All four subunits of the acetylcholine receptor (AChR) were found to incorporate label, with the gamma-subunit incorporating approximately 4 times as much as each of the other subunits. Carbamylcholine, an agonist, and histrionicotoxin, a noncompetitive antagonist, both strongly inhibited labeling of all AChR subunits in a specific and dose-dependent manner. In contrast, the competitive antagonist alpha-bungarotoxin and the noncompetitive antagonist phencyclidine had only modest effects on [125I]TID labeling of the AChR. The regions of the AChR alpha-subunit that incorporate [125I]TID were mapped by Staphylococcus aureus V8 protease digestion. The carbamylcholine-sensitive site of labeling was localized to a 20-kDa V8 cleavage fragment that begins at Ser-173 and is of sufficient length to contain the three hydrophobic regions M1, M2, and M3. A 10-kDa fragment beginning at Asn-339 and containing the hydrophobic region M4 also incorporated [125I]TID but in a carbamylcholine-insensitive manner. Two further cleavage fragments, which together span about one-third of the alpha-subunit amino terminus, incorporated no detectable [125I]TID. The mapping results place constraints on suggested models of AChR subunit topology.     

Planar bilayer membranes made from phospholipid monolayers form by a thinning process.

We investigated the manner in which planar phospholipid membranes form when monolayers are sequentially raised. Simultaneous electrical and optical recordings showed that initially a thick film forms, and the capacitance of the film increases with the same time course as the observed thinning. The diameter of fully thinned membranes varies from membrane to membrane and a torus is readily observed. The frequency-dependent admittance of the membrane was measured using a wide-bandwidth voltage clamp whose frequency response is essentially independent of capacitative load. The membrane capacitance dominates the total admittance and the membrane dielectric is not lossy. The specific capacitance of membranes of several mixtures was measured. A schematic diagram of the formation of these membranes is presented.     

Redox cycling and sulphydryl arylation; their relative importance in the mechanism of quinone cytotoxicity to isolated hepatocytes

Quinones are believed to be toxic by a mechanism involving redox cycling and oxidative stress. In this study, we have used 2,3-dimethoxy-1,4-naphthoquinone (2,3-diOMe-1,4-NQ), which redox cycles to the same degree as menadione, but does not react with free thiol groups, to distinguish between the importance of redox cycling and arylation of free thiol groups in the causation of toxicity to isolated hepatocytes. Menadione was significantly more toxic to isolated hepatocytes than 2,3-diOMe-1,4-NQ. Both menadione and 2,3-diOMe-1,4-NQ caused an extensive GSH depletion accompanied by GSSG formation, preceding loss of viability. Both compounds stimulated a similar increase in oxygen uptake in isolated hepatocytes and NADPH oxidation in microsomes suggesting they both redox cycle to similar extents. Further evidence for the redox cycling in intact hepatocytes was the detection of the semiquinone anion radicals with electron spin resonance spectroscopy. In addition we have, using the spin trap DMPO (5,5-dimethyl-1-pyrroline N-oxide), demonstrated for the first time the formation of superoxide anion radicals by intact hepatocytes. These radicals result from oxidation of the semiquinone by oxygen and further prove that both these quinones redox cycle in intact hepatocytes. We conclude that while oxidative processes may cause toxicity, the arylation of intracellular thiols or nucleophiles also contributes significantly to the cytotoxicity of compounds such as menadione.     

Enhanced carrier-mediated lactate entry into isolated hepatocytes from starved and diabetic rats

Hepatic plasma membrane lactate transport was studied in isolated hepatocytes prepared from fed, starved, and streptozotocin diabetic rats. Carrier-mediated lactate entry was determined using the lactate transport inhibitors alpha-cyano-3-hydroxycinnamate and D-3-hydroxybutyrate and was significantly greater in hepatocytes from starved compared to fed rats and in hepatocytes from diabetic fed compared to fed rats. The saturable component of lactate entry which corresponds to carrier-mediated transport was higher in the starved than in the fed state with results from diabetic fed being intermediate between the two. Insulin treatment prevented the increment in carrier-mediated lactate transport observed in hepatocytes from diabetic fed rats. The data indicate that hepatic plasma membrane lactate transport is increased under conditions of starvation and diabetes mellitus. This may partly explain the increased gluconeogenic flux under these conditions.