Synthesis of 1-(1-alkenyl)-2-acetyl-sn-glycero-3-phosphocholines, the aldehyded analogs of platelet activating factor

1-(1-Hexadecenyl)- and 1-(1-octadecenyl)-2-acetyl-sn-glycero-3-phosphocholines were synthesized. To this goal, synthetically prepared racemic phosphatidal-cholines were hydrolyzed with phospholipase A2, and lysophosphatidal-cholines obtained were acetylated with acetic anhydride.     

Two forms of glutamine synthetase in leaves of Cucurbita pepo

It has been shown that the leaves of pumpkin (Cucurbita pepo) contain two molecular forms of glutamine synthetase (GS), one occurring in the cytosol (GS₁)and the other in the chloroplasts (GS₂). The activities of both forms were greater when ammonium ion was infiltrated into the leaves and this was shown to be due to de novo synthesis. The two synthetases were purified by ammonium sulphate fractionation, ion exchange chromatography on DEAE-cellulose, selective adsorption on calcium phosphate gel, and preparative polyacrylamide gel electrophoresis. The MWs of GS₁ and GS₂, estimated by gel filtration on Sephacryl S-200, were 480 000 and 370 000 respectively. During polyacrylamide gel electrophoresis in the presence of SDS both GS₁ and GS₂ were dissociated into polypeptide chains with MWs of 58 000 and 50 000 respectively, suggesting that GS, ₁ and GS₂ are octamers consisting of identical monomers. The synthetases showed noticeable differences in their amino acid composition. In GS₁ and GS₂ the proportions of α- helical segments were 34 and 17 % respectively. In the presence of Mg²⁺, the pH optima for GS₁ and GS₂ were 7.25 and 7.75 respectively, and K_m values toward l-glutamate were 13 and 46 mM respectively. From the experimental data it is inferred that GS₁ and GS₂ are isoenzymes.     

Methionine Sulfoximine and Phosphinothrycin: A Review of Their Herbicidal Activity and Effects on Glutamine Synthetase

Derivatives of methionine sulfoximine (MSO) and phosphinothrycin (PPT), which are analogues of glutamate, exhibit selective herbicidal activity. This effect is accounted for by impairment of nitrogen metabolism, resulting from inhibition of its key enzyme in plants, glutamine synthetase (EC 6.3.1.2). Inhibition of the enzyme causes ammoniac nitrogen to accumulate and terminates the synthesis of glutamine. Changes in the content of these two metabolites (excess ammonium and glutamine deficiency) act in concert to cause plant death. However, low concentrations of MSO, PPT, and their metabolites produce an opposite effect: glutamine synthetase is activated, with concomitant stimulation of plant growth and productivity. The mechanisms whereby MSO and PPT affect glutamine synthetase activity are discussed in the context of nitrogen metabolism in plants.     

Inhibition of glutamine synthetase activity by biologically active derivatives of glutamic acid

The inhibition of activity of glutamine synthetase from Chlorella and porcine brain by 4-hydroxy-D-4-fluoro-D,L- and 4-amino-D,L-glutamic acids diastereoisomers was studied. Each compound was shown to exert the same inhibiting effect on glutamine synthetase from both sources. In case of threo-4-hydroxy-D-glutamic acid the inhibition of the Chlorella enzyme was of a competitive and of a completely mixed type. The enzyme inhibition by 4-fluoro-D, L-glutamic acids seemed to be of a completely non-competitive type. The Ki values for all inhibition reactions were determined. A comparison of biochemical parameters and biological activity revealed that the most effective inhibitors of the enzyme exert a most potent antitumour and antiviral action.     

Electron microscopy of glutamine synthetase from pea leaf chloroplasts

Using electron microscopy, the spatial structure of glutamine synthetase from pea leaf chloroplasts was studied. The enzyme was shown to consist of eight elongated subunits, which are arranged with a point of 42 symmetry at the vertices of two squares. These squares are twisted about a 4-fold axis at 40 degrees relative to each other.     

Mechanism of inhibition of pea chloroplast glutamine synthetase by methionine sulfoximine

In the presence of ATP and Mg2+ L-methionine sulfoximine irreversibly inhibits homogeneous glutamine synthetase (EC 6.3.1.2) from pea chloroplasts (I0.5 = 1.0 x 10(-7) M; Ki = 6.25 . 10(-8) M. Glutamate (but not NH4Cl) exerts a protective effect, which is enhanced when glutamate and NH4Cl are simultaneously present in the reaction mixture. The inhibiting action of L-methionine sulfoximine with respect to glutamate is of a mixed type. ATP and Mg-ATP produce the same non-competitive protective effect on L-methionine sulfoximine. The data obtained suggest that the formation of a quaternary complex (or a transition state) between the enzyme and all its substrates is essential for the catalysis.     

The Holocene climatic optimum at the southern coast of the Sea of Japan

Palynological spectra were studied from piston-cores of bottom sediments in the southwestern part of the Sea of Japan and the East Korea Bay. Five palynological assemblages were revealed in the sediments of the deep core and three, in the shelf core. The palynological assemblages were formed during different climatic phases and reflect main stages in the development of the vegetation of the region. The Holocene optimum was determined for the southern coast of the Sea of Japan.     

Effect of vagotomy, alpha-tocopherol and arachidene on lipid peroxidation in various areas of the gastroduodenal zone in rats with experimental peptic ulcer

Lipid peroxidation (LPO) was investigated in the mucosa of different gastroduodenal areas in rats with ulcer. The animals were subject to various types of vagotomy and given various drugs. The ulcerogenic agent--cystamine--was shown to have a different degree effect on the activation of free radical reactions, most pronounced in duodenal mucosa. Selective proximal vagotomy was most effective in decreasing LPO activity, as compared to total and partial vagotomy. The use of an antioxidant--alpha-tocopherol, particularly its combination with arachidene, a preparation of polyunsaturated fatty acids, prevented the development of duodenal ulcer in 75% of cases and markedly decreased both ascorbate- and NADP X H-dependent LPO. It is suggested that LPO is directly involved in the pathogenesis of ulcer and that factors attenuating the process of LPO may prevent ulcerogenesis.     

Preparation of affinity sorbents for the isolation of phospholipase A2

The preparation of biospecific organo-silica supports with different concentrations of covalently attached sn-glycero-3-phosphocholine was described. Sorbtion of phospholipase A2 on the hydrophobic analogues of biospecific supports was studied with the aim of elucidating the role of the enzyme-matrix hydrophobic interactions. A comparative characterization of the prepared sorbents was carried out.     

Biosynthetic paths of acyclic lipoxygenase metabolites of polyenic acids]

The review deals with the basic features of the fatty acid lipoxygenation resulting in the formation of leukotrienes, hydroxy fatty acids, lipoxins, hepoxylins. The biological role, prospects for the further studies of this class of bioregulators are discussed.