THE SPONTANEOUS RELEASE OF ACETYLCHOLINESTERASE IN RAT SUBSTANTIA NIGRA IS ALTERED BY LOCAL CHANGES IN EXTRACELLULAR LEVELS OF DOPAMINE

Acetylcholinesterase release in the guinea-pig substantia nigra has been previously investigated ‘on-line’, using a sensitive chemiluminescent system. Since histological observations suggest that there is a difference in acetylcholinesterase distribution in the rat substantia nigra compared to that of the guinea-pig, the first aim of the present study was to use this chemiluminescent method to characterise acetylcholinesterase release in this brain region of the freely moving rat, and the second was explore the relationship between acetylcholinesterase release and dopamine systems in this region. Accordingly, acetylcholinesterase release in the rat substantia nigra was studied under basal conditions of spontaneous release and following the local administration of (a) elevated potassium ions (30, 45, 60 mM), (b) a stimulator of dopamine/acetylcholinesterase release—D-amphetamine (10⁻⁷, 10⁻⁶ and 10⁻⁵ M), (c) an inhibitor of dopamine uptake—GBR12909 (10⁻⁷, 10⁻⁶ and 10⁻⁵ M). Spontaneous release of acetylcholinesterase in this brain region of the rat appears to be comparable with that observed in the guinea-pig, despite the smaller number of acetylcholinesterase-containing neurones. Furthermore, not only elevated potassium ions, but

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-amphetamine as well as GBR12909, all produced significant increases in the percentage spontaneous release of acetylcholinesterase. Thus, the release of acetylcholinesterase in this region may be triggered by levels of dopamine outside of the neurone. Copyright © 1996 Elsevier Science Ltd     

An efficient synthesis of methyl tetra-o-hexyl gentiooctaoside, an octaosyl analogue of ANP receptor antagonist HS-142-1

Methyl

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, a 3-O hexyl analogue of the octaosyl component of fungal lipooligosaccharide HS-142-1, was stereo- and regioselectively synthesized as a potent antagonist for the tetrameric atrial natriuretic peptide (ANP) receptors.     

The exopolysaccharides produced by Streptococcus thermophilus Rs and Sts have the same repeating unit but differ in viscosity of their milk cultures

The polysaccharides produced by Streptococcus thermophilus Rs and Sts in skimmed milk consist of -Gal and -Rha in a molar ratio of 5:2. Linkage analysis and 1D/2D NMR (¹H and ¹³C) studies revealed that both polysaccharides have the same branched heptasaccharide repeating unit:

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Remarkably, the two strains differ in their effects on the viscosity of stirred milk cultures. The milk culture of S. thermophilus Rs is non-ropy and affords 135 mg/L polysaccharide with an average molecular mass of 2.6×10³ kDa. In contrast, the milk culture of S. thermophilus Sts is ropy and produces 127 mg/L polysaccharide with an average molecular mass of 3.7×10³ kDa. Permeability measurements of non-stirred milk cultures of both strains suggest that both strains have a similar effect on the protein–polysaccharide network. Therefore, the only clear difference between both strains, which may cause the difference in ropiness of the milk cultures, is the difference in molecular mass of the polysaccharide.     

A stereocontrolled synthetic approach to glycopeptides corresponding to the carbohydrate-protein linkage region of cell-surface proteoglycans

The glycopeptides 1

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and 2

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), carrying the core structure of serine-linked cell-surface proteoglycans were synthesized in a stereocontrolled manner. The carbohydrate key imidate xylosyl donors 3 and glycotetraosyl donors 4 and 5, as well as a tetrapeptide glycosyl acceptor 6, were coupled in the crucial glycosylation step. In these reactions, the application of either trimethylsilyl trifluoromethanesulfonate (TMSOTf) or borontrifluoride etherate (BF₃-Et₂O) as catalysts proved to be highly efficient. The serine linked glycopeptides 34, 36 and 37 thus obtained yielded target compounds 1 and 2 on complete deprotection.     

Structural studies on [Mo3S4] and [Mo3S4Cu] complexes with tripodal ligands providing various NxOy (x + Y = 3) donor sets

The interaction of 1,3,5-triamino-1,3,5-trideoxy-cis-inositol (taci) and its N-methylated derivative 1,3,5-trideoxy-1,3,5-tris(dimethylamino)-cis-inositol (tdci) with the incomplete [Mo₃S₄]⁴⁺ cube and the heterometallic [Mo₃S₄Cu]⁴⁺ cube have been investigated by X-ray analysis. The crystal structures of [Mo₃S₄(taci+ rmC₃H₆O-H₂O)₃-4H]·2OH₂O (1a, rhombohedral, space group R32, A = 15.964(3), C = 40.59(1) Å, Z = 6), [Mo₃S₄(tdci)₃]Br₄·9.5EtOH·5H₂O (2a, triclinic, space group

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and [CuBrMo₃S₄(tdci)₃]Br₃·11 H₂O·EtOH (3a, monoclinic, space group P2,/n, A = 14.887(3), B = 22.570(4), C = 21.974(5) Å, β = 98.54(2)°, Z = 4) revealed andN-N-O and an N-O-O coordination mode for taci and tdci, respectively. In 1a, taci is coordinated as an anion with deprotonated oxygen and nitrogen donors. In addition, the non-coordinating amino group reacted with one equivalent; of acetone, forming a Schiff base condensation product. For 2a, short Mo---O bonds and high pK_a values (compared to the aqua ion [Mo₃S₄(H₂O)₉]⁴⁺) indicate the formation of a zwitterionic form of the tdci ligand with coordinated alkoxo groups and peripheral dimethylammonium groups. No significant differences were found for the structural properties of the Mo-tdci fragment in 2a and 3a. The coordination modes of taci and tdci, as observed in the solid state, are in agreement with the previously reported solution structures, established by NMR spectroscopy. They are attributed to the specific steric requirements of the two ligands and to a pronounced preference of the [Mo₃(μS)₃(μ₃S)]⁴⁺ core to coordinate a nitrogen donor trans to μ₃S.     

Formation of a metallocycle by dimerization of acrylonitrile. Crystal structure of the hexakis{(1,4-dicyanobutane-1,4-diyl)-nickel(II)} complex

A novel hexanickel(II) complex [Ni₆(NCCHCH₂CH₂CHCN)₆] (2) with 1,4-dicyanobutane-1,4-diyl (L) which was produced by the metal-induced dimerization of acrylonitrile (AN) has been isolated and the structure has been determined crystallographically. Complex 2 is triclinic, space group

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. Each nickel atom is coordinated by two carbon atoms of L and two nitrogen atoms of the cyano group of two other L, providing a square-plenar geometry. The six nickel atoms are bridged by the cyano group and carbon atom to form the slightly distorted octahedral Ni₆ core.     

The structure of the exopolysaccharide of Pseudomonas fluorescens strain H13

An acidic exopolysaccharide was isolated from P. fluorescens strain H13. The structure of the polysaccharide repeating unit was determined using chemical methods and 1D and 2D NMR techniques. The repeating unit was characterized as a trisaccharide composed of -glucose, 2-acetamido-2-deoxy- -glucose and

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acid.     

Structure determination of a novel uronic acid residue isolated from the exopolysaccharide produced by a bacterium originating from deep sea hydrothermal vents

The exopolysaccharide produced by the bacterium Alteromonas sp. strain 1644 originating from deep sea hydrothermal vents was shown to contain a novel glucuronic acid derivatives:

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acid. The structure of this compound was established on the basis of mass spectrometric data, methylation analysis, preparation of derivatives, and chemical synthesis of references compounds.     

The rhodium(III) trisacetonitrile complexes: a re-investigation of the synthesis of fac- and mer- [RhCl3(CH3CN)3], their characterization by 2D NMR spectroscopy and the X-ray crystal structure of mer-[RhCl3(CH3CN)3] · CH3CN

It is shown that the reaction of RhCl₃·3H₂O with acetonitrile normally produces mixtures of mer- and fac-[RhCl₃(CH₃CN)₃] (1a and 1b, respectively). The IR and ¹H NMR spectra of these isomers were re-investigated. Their two-dimensional (¹⁰³Rh,¹H) NMR spectra were also recorded. Equilibrium and exchange studies of 1a and 1b in CD₃C were performed. It was found that in 1a the exchange rate of the nitrile molecule trans to Cl is much faster than those of mutually trans nitriles. Also the nitrile molecules in 1b underwent fast exchange in CD₃CN; however, their rate was slightly faster than that of the more labile CH₃CN in 1a. The X-ray crystal structure of mer-[RhCl₃(CH₃CN)₃]·CH₃CN (1c) was determined. Crystal data: triclinic space group

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.     

Structure of an acidic microcapsular glycan from the reference strain (C.D.C. 866-57) for Serratia marcescens serogroup 01

The structure of the acidic polysaccharide from Serratia marcescens serogroup O1 has been investigated. NMR spectroscopy together with sugar and methylation analysis have been used as well as a uronic acid degradation. The polysaccharide consists of pentasaccharide repeating units having the following structure.

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The polysaccharide also contains one equivalent of O-acetyl groups per repeating unit present on, inter alia, a hydroxymethyl group.     

Transition behavior and phase structure of chitin/ poly(2-hydroxyethyl methacrylate) composites synthesized by a solution coagulation/bulk polymerization method

Chitin/poly(2-hydroxyethyl methacrylate) (PHEMA) composites were synthesized via photo-polymerization in a gel state of chitin swollen with HEMA monomer as reactive impregnant. The transition behavior and phase structure of the chitin/PHEMA composites were characterized by differential scanning calorimetry, dynamic viscoelastic analysis, and solid-state ¹³C NMR spectroscopy. For compositions containing 20wt% chitin, it was reasonably assumed that an original network structure of chitin gels was sufficiently perpetuated into the cross-linked PHEMA matrix, resulting in the formation of an interpenetrating polymer network (IPN) type organization. Owing to this IPN effect, the lowering of the dynamic modulus É of the composites in the glass transition temperature region was extremely suppressed, compared with the corresponding

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E" height="15" width="11">-drop observed for plain PHEMA samples. From measurements of the proton spin-lattice relaxation times t_1ρ^h in the NMR study, the IPN-like composites were estimated to be homogeneous on a scale of less than ˜2.4nm.     

N-Carboxyacyl analogues of CCK with a substituted Gly: Interaction with pancreatic and gallbladder CCK receptors

It has been reported that certain N-carboxyacyl analogues of CCK-8 and of CCK-7 with a substituted Gly in position 3 or 4 of the peptide possess higher potencies at stimulating pancreatic enzyme secretion than at stimulating gallbladder contraction, suggesting that these analogues are able to differentiate subtypes of CCK_A receptors. However, no studies examined directly the interaction of these peptides with the CCK receptors in both tissues. In the present study, CCK-8 and various N-carboxyacyl analogues of CCK-7 and of CCK-8 were prepared by solid phase synthesis using Fmoc chemistry and were purified by HPLC; molecular weight and sufficient sulfation were determined by mass spectrometry. [¹²⁵I]Bolton-Hunter(BH)-CCK-8 binding to sections of the guinea pig pancreas and gallbladder was determined under identical conditions; amylase release from pancreatic acini and contraction of gallbladder muscle strips were measured in vitro. Each peptide stimulated amylase release (EC₅₀):

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). The same relative potencies were found for stimulation of gallbladder contraction, and for the inhibition of [¹²⁵I]BH-CCK-8 binding to pancreas and gallbladder sections. These data demonstrate that the CCK_A receptors in the pancreas and on gallbladder smooth muscle possess similar affinities for the various N-carboxyacyl analogues of CCK-7 and CCK-8 with a substituted Gly and provide further evidence that the CCK_A receptors in gallbladder and pancreas cannot be distinguished pharmacologically.     

Lipid composition of adult Foleyella agamae

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& Obiamiwe B. A. 1986. Lipid composition of adult Foleyella agamae. International Journal for Parasitology 16: 655–657. The lipid and fatty acid composition of the filarial parasite Foleyella agamae were investigated. Total lipids accounted for 7.05% of the parasite fresh weight. Neutral lipids comprised 56.34% of the total and polar lipids 43.66%. The major lipid classes detected include sterol esters, cholesterol, phosphatidyl choline and phosphatidyl ethanolamine. Fatty acids varying in chain length from 10 carbon atoms through 20 carbon atoms were identified in the total lipid extract. The 18 carbon fatty acids formed the predominant components. The 20 carbon fatty acids were confined to the polar lipds.     

Cyclic analogues of Tyr-W-MIF-1 with prolonged analgesic activity and potency comparable to DAMGO and morphine

Two cyclic analogues of the brain peptide Tyr-W-MIF-1 (Tyr-Pro-Trp-Gly-NH₂) were synthesized and tested for analgesic activity in the rat tail flick test after intracerebroventricular (ICV) injection. The analogues were about 200-fold more potent than the parent peptide. Analgesia was dose dependent, and at 1 μg the two analogues, the mu-selective enkephalin analogue DAMGO (

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), and morphine, all produced analgesia lasting between 40 and 60 min. Analgesia of longer duration was evident at higher doses of the analogues and lasted more than 6 h after 100 μg, the highest dose tested. The results show that peptide analogues based on the structure of the endogenously occurring Tyr-W-MIF-1 can produce potent and long-lasting effects on nociception.     

The impact of aromatase mechanism on other P450s

Experimental findings from a number of laboratories have converged to show that the conversion of androgens into oestrogen, catalysed by aromatase, involves three distinct reactions which occur at a single active site. That each one of these reactions belongs to a different generic type was revealed by chemical consideration, together with our ¹⁸O-experiments. In particular, these findings high-lighted the fact that the third reaction in the sequence occurs by a novel process for which a number of plausible mechanisms have been considered. The scrutiny of these mechanisms has involved either studies on aromatase itself, or on related enzymes which catalyse the aromatase type of cleavage reaction as generalized in equation 1:

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The acyl-carbon cleavage reaction of equation 1 is catalysed by sterol 14-demethylases, accounts for several side-chain fission products formed by CYP17 (17-hydroxylase-17,20-lyase), and constitutes a weak property of certain drug metabolizing P450s, when given aliphatic aldehydes as substrates. From cumulative studies on these enzymes, consensus is beginning to emerge that the acyl-carbon fission may be promoted by the Fe^III---OOH intermediate, formed during the catalytic cycles of P450s. The precedent for the direct involvement of the Fe^III---OOH species in the reaction of equation 1 is influencing our thinking regarding the mechanism of the conventional hydroxylation reaction. The status of knowledge surrounding the current debate on these issues will be reviewed.     

The PHBH fold: Not only flavoenzymes

p-Hydroxybenzoate hydroxylase,

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-amino acid oxidase, cholesterol oxidase and glucose oxidase form a family of structurally related flavoenzymes. Comparison of their three-dimensional structures reveal how the same FAD-binding scaffold has been employed to implement diverse active-site architectures, suited for different types of catalytic reactions. The substrate binding mode differs in each of these enzymes, with the catalytically relevant residues not located on homologous positions. A common feature is provided by the ability of these enzyme to bury their substrates beneath the protein surface. In

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-amino acid oxidase and cholesterol oxidase, a loop forms a ‘lid’ controlling the active site accessibility, whereas in p-hydroxybenzoate hydroxylase is the flavin itself, which swings out to allow substrate binding. The crystallographic analysis has revealed that the GTP-dissociation inhibitor of RAB GTPases has a folding topology remarkably similar to p-hydroxybenzoate hydroxylase. This finding highlights the versatile nature of this folding topology, which in addition to flavin-dependent catalysis, is suited for diverse functions, such as the regulation of GTPases.     

Synthesis, crystal structure and magnetic properties of the chiral iron(II) chain [Fe(bpym)(NCS)2]n (bpym = 2,2′-bipyrimidine)

The iron(II) compound of formula [Fe(bpym)(NCS)₂]_n (bpym = 2,2′-bipyrimidine) has been synthesized and its crystal structure determined by X-ray diffraction methods. It crystallizes in the tetragonal P4₁ (No. 76) and P4₃ space groups, a = 8.849(2), C=16.486(3) Å, V=1290.9(5) ų, Z=4, D_c=1.699 g cm⁻³, M_r=330.2, F(000)=664, λ(Mo K)=0.71073 Å, μ(Mo K)=14.8 cm⁻¹ and T=295 K. A total of 2449 reflections was collected over the range 3≤2≤55°; of these, 1657 were unique and 1321 were considered as observed (13σ(I)) and used in the structural analysis. The final R and R_w residuals were 0.027 and 0.026, respectively. The structure is made up of chiral (Δ and Λ enantiomers crystallize in the same crop) chains of iron(II) atoms bridged by bis-chelating bpym, the electroneutrality being achieved by N-bonded thiocyanato groups in cis position. Each metal atom is in a distorted FeN₆ octahedral environment, the Fe---N bonds ranging from 2.265(3) to 2.028(4) . The intrachain metal-metal separation is 5.960(1) Å. Variable-temperature magnetic susceptibility data in the temperatyre range 290–4.2 K show that the iron(II) is high-spin and interacts in an antiferromagnetic fashion, the relevant parameters being

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. The magnitude of the exchange coupling compares well with that reported for other structurally characterized bpym-bridged iron(II) complexes.     

Determination of the structure of a fucose-containing trisaccharide monophosphate isolated from human pregnancy urine

A new acidic oligosaccharide, isolated from the urine of a pregnant women by gel filtration and ion-exchange chromatography, was shown on the basis of sugar analysis, methylation analysis, exo-glycosidase digestion, e.i.-m.s., f.a.b.-m.s., and n.m.r. spectroscope to have the following structure:

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Olefin versus sulfur coordination of benzo[b]thiophene (BT) in Cp(CO)2Re(η:η-μ2-BT)Cr(CO)3

Reactions of Cr(CO)₃(η⁶-BT), in which the Cr is π-coordinated to the benzene ring of benzo[b]thiophene (BT), with Cp′(CO)₂Re(THF), where Cp′ = η⁵-C₅H₅ or η⁵-C₅Me₅, give the products Cp′(CO)₂Re(η²:η⁶-μ₂-BT)Cr(CO)₃ in which the Cr remains coordinated to the benzene ring and Re is bound to the C(2)=C(3) double bond. An X-ray diffraction study of Cp(CO)₂Re(η²:η⁶-μ₂-BT)Cr(CO)₃ (3) provides details of the geometry. This structure contrasts with that of the Cp′(CO)₂Re(BT) complexes that exist as mixtures of isomers in which the BT is coordinated to the Re through either the double bond (2,3-η²) or the sulfur (η¹(S)). Thus, the electron-withdrawing Cr(CO)₃ group in 3 stabilizes the 2,3-η² mode of BT coordination to the Cp′(CO)₂Re fragment. Implications of these results for catalytic hydrodesulfurization of BT are discussed. Crystal data for 3: triclinic, space group

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.     

Coordination modes of the novel bifunctional nitrogen ligands 8-(2-pyridyl)quinoline and 8-(6-methyl-2-pyridyl)quinoline towards palladium and platinum. X-ray crystal structures of (8-(2-pyridyl)quinoline)Pd(Me)Cl, (8-(2-pyridyl)quinoline)-Pd(C(O)Me)Cl and (8-(2-pyridyl)quinoline)Pd(PEt3)Cl2

The coordination chemistry of the new bidentate nitrogen ligands 8-(2-pyridyl)quinoline (8-PQ) and 8-(6-methyl-2-pyridyl)quinoline (Me-8-PQ) towards palladium and platinum has been studied. Several (NN)Pd(R)Cl and (NN)Pd(alkene) complexes have been synthesized. The complex (8-PQ)Pd(Me)Cl has been characterised by a single crystal X-ray determination (crystal data triclinic space group

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). A fast CO insertion occurs into the palladium-carbon bond of the complexes (NN)Pd(Me)Cl providing the (NN)Pd(C(O)Me)Cl complexes. For (8-PQ)Pd(C(O)Me)Cl an X-ray structure determination has been carried out (crystal data: monoclinic space group P2₁/c with a=9.084(4), B=10.179(3), C=16.400(3) Å, β=95.59(2)°, V=1509.2(9) ų, R=0.043, Z=4). Unexpected in both molecular structures is the large dihedral angle between the plane of the bidentate nitrogen ligand and the coordination plane of the palladium. Both bidentate coordinating ligands 8-PQ and Me-8-PQ show a relatively large bite angle. A monodentate coordination mode has been observed for the complexes (NN)M(PEt₃)Cl₂ (M=Pd, Pt), as the pyridyl group of the ligand is coordinated to the metal while the quinoline group is dissociated from the metal, which is shown in the X-ray structure determination for the complex (8-PQ)Pd(PEt₃)Cl₂ (crystal data: monoclinic space group P2₁/a with A=15.736(2), B=7.782(1), C=18.255(3) Å, β=102.98(1)°, V=2178.3(6) ų, R=0.062, Z=4).