Synthesis and pharmacological evaluation of combined Thromboxane receptor antagonists/thromboxane synthase inhibitors: Pyridine-containing amino-prostanoids

Incorporation of a pyridine miety into amino-prostanoids, previously shown to be thromboxane receptor antagonists, has provided a series of compounds which also show potent thromboxane synthase inhibitory activity. GR 83783, an ⁿpropyl-substituted pyridine demonstrates these properties both in vitro and in vivo.     

The structure of the egg-shell of Porrocaecum ensicaudatum (Nematoda: Ascaridida)

Wharton D. A. 1979. The structure of the egg-shell of Porrocaecum enslcaudatum (Nematoda: Ascaridida). International Journal for Parasltology9: 127–131. The egg-shell of Porrocaecum ensicaudatum is oval with an opercular plug at either end. The shell consists of three layers: an inner lipid layer, a middle chitinous layer and an outer vitelline layer. The vitelline layer has strands of particulate material attached to its outer surface. The chitinous layer consists of 8.5 nrn fibrils which are made up of a chitin microfibril core surrounded by a protein coat. The fibrils are oriented randomly or in parallel, there being no indication of helicoidal architecture.The chitinous layer varies in thickness to form a pattern of interconnecting ridges on the surface of the egg. This pattern presumably increases the shell's structural strength.     

Substituting an alpha-helix switches the sequence-specific DNA interactions of a repressor

It has been suggested that many DNA-binding proteins use an alpha-helix for specific sequence recognition. We have used amino acid sequence homologies to identify the presumptive DNA-recognition helices in two related proteins whose structures are unknown--the repressor and cro protein of bacteriophage 434. The 434 repressor and cro protein each bind to three similar sites in the rightward phage 434 operator, OR, and they make different contacts in each binding site, as revealed by the chemical probe dimethyl sulfate. We substituted the putative recognition alpha-helix of 434 repressor with the putative recognition alpha-helix of 434 cro protein to create a hybrid protein named repressor*. The specific DNA contacts made by repressor* are like those of 434 cro protein.     

Hormonal regulation of discrete portions of the cell cycle: commitment to DNA synthesis is commitment to cellular division

Density-arrested human fibroblasts were stimulated to traverse G0/G1 and initiate DNA synthesis by the addition of medium containing either serum or a combination of platelet-derived growth factor and platelet-poor plasma. Medium containing a combination of epidermal growth factor and high concentrations of insulin also stimulated DNA synthesis in platelet factor-treated quiescent cells. Platelet factor was required only to initiate proliferation. Epidermal growth factor and insulin then allowed G1 traverse and commitment to DNA synthesis. Cells could complete S, G2, and M in unsupplemented medium lacking peptide growth factors.     

Consequences of molecular recognition in the S1-S2 intersubsite region of papain for catalytic-site chemistry. Change in pH-dependence characteristics and generation of an inverse solvent kinetic isotope effect by introduction of a P1-P2 amide bond into a two-protonic-state reactivity probe.

1. The pH-dependences of the second-order rate constant (k) for the reactions of papain (EC 3.4.22.2) with 2-(acetamido)ethyl 2'-pyridyl disulphide and with ethyl 2-pyridyl disulphide and of k for the reaction of benzimidazol-2-ylmethanethiol (as a minimal model of cysteine proteinase catalytic sites) with the former disulphide were determined in aqueous buffers at 25 degrees C at I 0.1. 2. Of these three pH-k profiles only that for the reaction of papain with 2-(acetamido)ethyl 2'-pyridyl disulphide has a rate maximum at pH approx. 6; the others each have a rate minimum in this pH region and a rate maximum at pH 4, which is characteristic of reactions of papain with other 2-pyridyl disulphides that do not contain a P1-P2 amide bond in the non-pyridyl part of the molecule. 3. The marked change in the form of the pH-k profile consequent upon introduction of a P1-P2 amide bond into the probe molecule for the reaction with papain but not for that with the minimal catalytic-site model is interpreted in terms of the induction by binding of the probe in the S1-S2 intersubsite region of the enzyme of a transition-state geometry in which nucleophilic attack by the -S- component of the catalytic site is assisted by association of the imidazolium ion component with the leaving group. 4. The greater definition of the rate maximum in the pH-k profile for the reaction of papain with an analogous 2-pyridyl disulphide reactivity probe containing both a P1-P2 amide bond and a potential occupant for the S2 subsite [2-(N'-acetyl-L-phenylalanylamino)ethyl 2'-pyridyl disulphide [Brocklehurst, Kowlessur, O'Driscoll, Patel, Quenby, Salih, Templeton, Thomas & Willenbrock (1987) Biochem. J. 244, 173-181]) suggests that a P2-S2 interaction substantially increases the population of transition states for the imidazolium ion-assisted reaction. 5. The overall kinetic solvent 2H-isotope effect at pL 6.0 was determined to be: for the reaction of papain with 2,2'-dipyridyl disulphide, 0.96 (i.e. no kinetic isotope effect), for its reaction with the probe containing only the P1-P2 amide bond, 0.75, for its reaction with the probe containing both the P1-P2 amide bond and the occupant for the S2 subsite, 0.61, and for kcat./Km for its catalysis of the hydrolysis of N-methoxycarbonylglycine 4-nitrophenyl ester, 0.67.(ABSTRACT TRUNCATED AT 400 WORDS)     

Recognition of DNA sequences by the repressor of bacteriophage 434

The structure of a complex between the DNA-binding domain of phage 434 repressor and a 14 base-pair synthetic DNA operator reveals the molecular interactions important for sequence-specific recognition. A set of contacts with DNA backbone, notably involving hydrogen bonds between peptide-NH groups and DNA phosphates, position the repressor and fix the DNA configuration. Direct interactions between amino acid side chains and DNA bases involve nonpolar van der Waals contacts as well as hydrogen bonds. The structures of the repressor domain and of the 434 cro protein are extremely similar. There appear to be no major conformational changes in the proteins when they bind to DNA.     

Ventricular and atrial myocytes of newborn rats synthesise and secrete atrial natriuretic peptide in culture: Light-and electron-microscopical localisation and chromatographic examination of stored and secreted molecular forms

Summary We have demonstrated that atrial natriuretic peptide-like immunoreactivity is stored and secreted by ventricular and atrial myocytes in dissociated cell culture preparations from the heart of newborn rat. Culture preparations were maintained in either foetal calf serum-supplemented medium 199 or in hormone-supplemented, serum-free medium 199. The presence of atrial natriuretic peptidelike immunoreactivity in the cultured myocytes was demonstrated at both light-and electron-microscopical levels. Release of atrial natriuretic peptide-like immunoreactivity into the culture medium was measured by radioimmunoassay; molecular forms of the stored and secreted peptide were determined by gel column chromatography. The atrial natriuretic peptide-like immunoreactivity of cultured atrial and ventricular myocytes was concentrated in the perinuclear cytoplasm and was localised to electron-dense secretory granules. The number of immunoreactive ventricular myocytes and the intensity of their immunofluorescence changed with time in culture and was higher in cultures in foetal calf serum-supplemented medium than in serum-free medium. Gamma-atrial natriuretic peptide was stored and released by cultured atrial and ventricular myocytes, but was broken down to alpha-atrial natriuretic peptide in the growth medium. This process was foetal calf serum-independent, since it occurred in both the media used, indicating that cardiac myocytes in culture may release a factor that cleaves gamma-atrial natriuretic peptide to form alphaatrial natriuretic peptide.