Acceptor Reaction Research Articles

Das Levonorgestrel-Intrauterinpessar

The levonorgestrel IUD offers a valuable improvement for women, who develop menorrhagia with conventional IUDs. However, since the levonorgestrel Nova-T induces amenorrhea and spotting in a substantial proportion of the patients, it is advisable, before insertion, to evaluate the acceptor's reaction to the "new" bleeding pattern induced by the steroid IUD.

Electron transfer reactions catalyzed by the iron-sulfur cluster, (n-Bu 4N) 2[Fe 4S 4(SCH 2CONH 2) 4], in 90% DMF-10% H 2O

The synthetic iron-sulfur cluster, (n-Bu 4N) 2[Fe 4S 4(SCH 2CONH 2) 4] was newly prepared and its catalytic effect on the electron transfer reaction was investigated. The results demonstrated that the present iron-sulfur cluster actually accelerated the electron transfer reactions from a mercaptan to various types of organic electron acceptors in homogeneous DMF-H 2O solution. The linear free energy relationship which was found between the redox potentials of the acceptors and the reaction rates suggested that a single-electron transfer mechanism operated in the reactions of electron acceptors having fairly wide range of redox potentials.

The Generation of Singlet Oxygen (1O2) by the Nitrodiphenyl Ether Herbicide Oxyfluorfen Is Independent of Photosynthesis

The mechanism of action of the p-nitrodiphenyl ether herbicides has remained ambiguous because of conflicting reports in the literature. The diphenyl ether herbicide oxyfluorfen causes a light induced consumption of oxygen which resembles the electron acceptor reaction of paraquat. However, this reaction is not linked to the transport of electrons through photosystem I. This conclusion is based on the observation that the rate of oxygen consumption, in the presence of oxyfluorfen, does not demonstrate a first order rate dependence on light intensity. Using the bleaching of N,N-dimethyl p-nitrosoaniline as a specific detector of singlet oxygen, we demonstrate that oxyfluorfen is a potent generator of this toxic radical. The production of singlet oxygen occurs in the presence of inhibitors of photosynthetic electron transport (oxyfluorfen at 10(-4) molar and paraquat) and also under temperature conditions (3 degrees C) which prevent electron transport. This light induced reaction results in oxygen consumption and is the primary cause of lethality for oxyfluorfen. The production of singlet oxygen occurs rapidly and at low herbicide concentrations (10(-9) molar). The reaction occurs without photosynthetic electron transport but does require an intact thylakoid membrane.

Effect of borate ions on dextransucrase acceptor reaction

The effect of borate ions on the acceptor-reaction products of theLeuconostoc mesenteroides B-512F dextransucrase is described. Fructose released during the enzymatic reaction, is complexed with borate ions. this avoids its acceptor effect with the glucosyl-enzyme complex, which results in the synthesis of leucrose and isomaltulose by-products. A significative increase in dextran yield is thus obtained. The decrease in by-products concentration during the synthesis of high molecular weight dextrans is quantified.

Reaction of Hydroxide Ion with Electron Acceptors in Dimethyl Sulfoxide

Abstract In dimethyl sulfoxide, the reaction of hydroxide ion with several electron acceptors—iodine, tetracyanoquinodimethan, Nitro Blue Tetrazolium chloride, 2,3,5-triphenyltetrazolium chloride, anthraquinone, and benzophenone—gave reaction products identical to those obtained by the reaction of these electron acceptors with electron donors. The reaction pathways of these electron acceptors were found to be composed of successive one-electron reactions similar to the electrochemical reduction of these electron acceptors. These results indicate that hydroxide ion acts as a reductant in dimethyl sulfoxide.

Inhibition- and acceptor-reaction studies of streptococcus mutans 6715 glucosyltransferases with 3-deoxysucrose, 3-deoxy-3-fluorosucrose, and α- dallopyranosyl β- d-fructofuranoside

Three new sucrose analogs modified at C-3 have been studied as inhibitors and substrates for the glucosyltransferases (glucansucrases) of Steptococcus mutans 6715. Although none of the analogs were found to be substrates for polymer synthesis with either the soluble-polysaccharide producing enzyme, GTF-S, or the insoluble-polysaccharide producing enzyme, GTF-I, 3-deoxysucrose and 3-deoxy-3-fluorosucrose were able to donate glycosyl residues for acceptor reactions with both enzymes. Modification at C-3 considerably decreased the binding at the active site of both enzymes, since all of the analogs had inhibition constants at least one order of magnitude greater than the K m value for sucrose.

Acceptor reaction of a highly purified dextransucrase with maltose and oligosaccharides. Application to the synthesis of controlled-molecular-weight dextrans

Kinetic studies and product characterization of the acceptor reaction of a highly purified dextransucrase isolated from cultures of Leuconostoc mesenteroides suggested that the introduction of increasing amounts of maltose in the medium of reaction produced an increase of the kinetic constants, K′ m and V max, of the enzyme for sucrose. A Box-Hunter mathematical optimization concerning the products of the reaction with maltose showed that the sucrose-to-maltose ratio is of prime influence upon the yield of the oligosaccharides produced and that their weight-average molecular weight ( M w) is a linear function of that ratio. In view of directly synthesizing controlled-molecular-weight dextrans, various populations of oligosaccharides were produced and used as glucosyl acceptors in a second-step reaction with sucrose. The molecular weight and polydispersity of the second-step products were related to the sucrose-to-acceptor ratio and to the characteristics of the oligosaccharide acceptor.

The slow rate of proton consumption at the reducing side of Photosystem I is limited by the rate of redox reactions of extrinsic electron acceptors, but not by a diffusion barrier for protons

Absorption changes of cresol red at 575 nm which indicate proton consumption in the external bulk phase were measured under repetitive flash excitation of pea thylakoids. In the presence of methyl viologen as terminal electron acceptor, proton consumption due to the activity of both photosystems was slow with a half-rise time of 130 ms. If either superoxide dismutase was added or the natural acceptor system was complemented by addition of ferredoxin and NADP +, the rise of the alkalization was accelerated and two phases became distinguishable: a slow phase which was due to Photosystem II activity ( t 1 2 ≈ 100 ms ) and a fast phase which was due to Photosystem I activity. In the presence of the artificial electron acceptor methyl viologen, the rise of the fast phase was accelerated in proportion to the amount of added superoxide dismutase to a limit of t 1 2 = 10 ms . From these results we concluded that the slow rate of proton consumption at the reducing side of Photosystem I was limited by the nature of the supplied acceptor system, but not predominantly by a diffusion barrier for protons.

Activity of branched dextrans in the acceptor reaction of a glucosyltransferase (GTF-I) from Streptococcus mutans OMZ176

The ability of several native and chemically synthesized, branched dextrans to stimulate the activity of an α- d-glucosyltransferase (GTF-I) of Streptococcus mutans has been compared. The enzyme catalysed the transfer of glucosyl residues from sucrose with the formation of water-insoluble (1→3)-α- d-glucan. The rate of this reaction was greatly increased in the presence of dextran, and the extent of stimulation was negatively correlated with the degree of branching of the added dextran. The results refute the concept that growth of water-insoluble glucan occurs from the multiple, non-reducing termini of dextran acceptors.

Activation and inhibition of dextransucrase by calcium

Initial rate kinetics of dextran synthesis by dextransucrase (sucrose:1,6α- D-glucan-6-α- D-glucosyltransferase, EC 2.4.1.5) from Leuconostoc mesenteroides NRRL B-512F showed that below 1 mN, Ca 2+ activated the enzyme by increasing V max and decreasing the K m for sucrose. Above 1 mM, Ca 2+ was a weak competitive inhibitor ( K i = 59 mM. Although it was an activator at low concentration, Ca 2+ was not required for dextran synthesis, either of main chain or branch linkages. Neither was it required for sucrose hydrolysis, acceptor reactions, or enzyme renaturation after SDS-polyacrylamide gel electrophoresis. A model for dextran synthesis is proposed in which dextransucrase has two Ca 2+ sites, one activating and one inhibitory. dextran synthesis is proposed in which dextransucrase has two Ca 2+ sites, one activating and one inhibitory. Ca 2+ at the inhibitory site prevents the binding of sucrose.

A stereospecific palladium mediated [3+2] cycloaddition

The [3+2] palladium mediated cycloaddition to methyl ( E )- and ( Z ) - (R)-4/5-di-O-isopropylidene-pent-2-enoates parallels the Diels-Alder reactions of these same acceptors.

REACTION OF HYDROXIDE ION WITH ELECTRON ACCEPTORS IN ACETONITRILE

Abstract The reaction of hydroxide ion with electron acceptors gave reaction products identical to those obtained by the reaction of these electron acceptors with electron donors. The results indicate that hydroxide ion works as a reductant in acetonitrile.

Relative, quantitative effects of acceptors in the reaction of Leuconostoc mesenteroides B-512F dextransucrase

The acceptor reaction of dextransucrase consists of the transfer of d-glucosyl groups from sucrose to other carbohydrates, and occurs at the expense of dextran synthesis. In the present study, solutions of [14C]sucrose and of each of seventeen acceptor sugars were digested with highly purified Leuconostoc mesenteroides B-512F dextransucrase. The products were separated by paper chromatography, and quantitated by liquid scintillation counting. Maltose was the most effective acceptor; its products, members of an isomaltodextrinyl-maltose series (d.p. 3 to 6), accounted for >75% of the d-glucosyl groups of sucrose. Other acceptors giving rise to a similar series of oligosaccharide products were (in order of decreasing effectiveness): isomaltose, nigerose, methyl α-d-glucoside, 1,5-anhydro-d-glucitol, d-glucose, turanose, methyl β-d-glucoside, cellobiose, and l-sorbose. Lactose, raffinose, melibiose, d-galactose, and d-xylose each gave a single, mono-d-glucosylated product; d-fructose and d-mannose each gave a pair of mono-d-glucosylated (disaccharide) products. Another series of digests contained sucrose and various proportions of maltose. As the level of maltose increased, the size of the largest oligosaccharide acceptor-product decreased, and less dextran was produced. The virtual absence of high-d.p. (8 to 13) oligosaccharide products in all acceptor digests is interpreted as evidence against a role for acceptors as primers of dextran synthesis.

The formation of α- d-(1→3) branch linkages by an exocellular glucansucrase from Leuconostoc mesenteroides NRRL B-742

Leuconostoc mesenteroides NRRL B-742 produces two exocellular α- d-glucans, namely, fraction L, which consists of an α- d-(1→6) backbone with α- d-(1→4) branch-points, and fraction S, which consists of an α- d-(1→6) backbone with α- d-(1→3) branch-points. It was found that the percentage of α- d-(1→3) branch-points in fraction S glucan is variable, depending on the conditions under which it is synthesized from sucrose by the exocellular glucansucrase, and that α- d-(1→3) branch formation by this glucansucrase occurs by acceptor reactions in which α- d-glucosyl groups are transferred from sucrose to OH-3 groups on α- d-(1→6)-linked d-glucan chains. Thus, any change in reaction conditions that affects the rate of acceptor reactions relative to chain elongation also affects the degree of branching in B-742 fraction S dextran. It was also found that this glucansucrase is capable of modifying other dextrans, such as B-512F and B-742 fraction L, by transferring d-glucosyl groups to OH-3 of d-glucosyl residues in these dextrans as well.

Pairing reactions of interstitial cobalt and shallow acceptors in silicon observed in Mössbauer spectroscopy

Cobalt in silicon dissolves mainly interstitially. For shallow acceptor concentrations larger than 1016 atoms cm-3 the formation of pairs of interstitial cobalt and negatively charged boron, aluminium and gallium acceptors is observed by Möβbauer spectroscopy. The cobalt acceptors pairs anneal out between 100 °C and 250 °C. The dissociation of the pairs and the precipitation of isolated interstitial cobalt occur simultaneously. The binding energies for the cobalt aluminium and cobalt gallium pairs are higher than for the cobalt boron pair. The Möβbauer spectra of the cobalt acceptor pairs are fitted by two or three doublets whose relative intensity varies with temperature. A tentative microscopic model is proposed. The existence of pairs with shallow acceptors implies that interstitial cobalt possesses a donor level.

Acceptor reactions of alternansucrase from Leuconostoc mesenteroides NRRL B-1355

Extracellular glucansucrases from various bacterial sources, including Leuconostoc mesenteroides, have been shown to catalyze the transfer of glucosyl groups from sucrose to low-molecular-weight acceptor sugars, forming a series of oligosaccharides. An extracellular glucansucrase recently isolated from Leuconostoc mesenteroides NRRL B-1355 synthesizes a polysaccharide consisting of alternating α-(1→6)- and α-(1→3)-linked d-glucose residues. We have found that this enzyme preparation is capable of forming both α-(1→6)- and α-(1→3)-linked acceptor-products in the presence of a number of low-molecular-weight acceptor sugars. d-Glucose gave isomaltose only, no nigerose being formed. Similarly, methyl α- d-glucoside, methyl β- d-glucoside, maltose, and nigerose gave methyl α-isomaltoside, methyl β-isomaltoside, panose, and 6 2- O-α- d-glucosylnigerose, respectively. However, isomaltose gave both isomaltotriose and 3 2- O-α- d-glucosylisomaltose. These initial acceptor-products may also act as acceptors, and the structures of the products of higher d.p. show that a (1→3)-α- d-glucosidic bond is formed only when the nonreducing glucose acceptor group is linked through an α-(1→6) bond to another glucose residue. Experiments using [ 14C]sucrose and unlabeled acceptors showed that acceptor reactions occur by transfer of a glucosyl group from sucrose to O-3 or O-6 of the glucosyl group at the nonreducing end of the acceptor saccharide. If a “good” acceptor is defined as one that gives rise to a greater amount of oligosaccharide and less polysaccharide, then the acceptors tested may be listed as follows: maltose ≥ nigerose > methyl α- d-glucoside > isomaltose > d-glucose > methyl β- d-glucoside.

Kinetics and mechanism of the reactions of alkyl-radical-acceptor inhibitors with hydrocarbon hydroperoxides

1. Rate constants have been determined for the reaction of alkyl-radical acceptors, N-naphthyl-N′-phenyl-p-quinonediimine (QD), 3,6-di-tert-butyl-o-benzoquinone (DTBQ), p-benzoquinone (BQ), and 2,2,6,6-tetramethyl-4-benzoylpiperidine-1-oxyl (>NO.) with 1-nonene and ethylbenzene hydroperoxides at 120‡C. 2. The reactions of alkyl-radical acceptors with hydroperoxides reduce the activity of these compounds as antioxidants. 3. The stoichiometric coefficient for QD inhibition in the reaction with 1-nonene alkyl radicals has a value of 2. 4. Rate constants have been determined for the overall breakdown, and for the breakdown with radical formation, of 1-nonene hydroperoxide at 120‡C.

ChemInform Abstract: STUDY OF THE REACTION OF 10‐VINYLPHENOTHIAZINE WITH ORGANIC ELECTRON ACCEPTORS. II. UNCONVENTIONAL COURSE OF THE REACTION OF 10‐VINYLPHENOTHIAZINE WIT TETRAHALOBENZOQUINONES IN BENZENE

Chemischer InformationsdienstVolume 12, Issue 11 Heterocyclic Compounds ChemInform Abstract: STUDY OF THE REACTION OF 10-VINYLPHENOTHIAZINE WITH ORGANIC ELECTRON ACCEPTORS. II. UNCONVENTIONAL COURSE OF THE REACTION OF 10-VINYLPHENOTHIAZINE WIT TETRAHALOBENZOQUINONES IN BENZENE A. G. GORSHKOV, A. G. GORSHKOVSearch for more papers by this authorV. K. TURCHANINOV, V. K. TURCHANINOVSearch for more papers by this authorG. N. KUROV, G. N. KUROVSearch for more papers by this authorG. G. SKVORTSOVA, G. G. SKVORTSOVASearch for more papers by this author A. G. GORSHKOV, A. G. GORSHKOVSearch for more papers by this authorV. K. TURCHANINOV, V. K. TURCHANINOVSearch for more papers by this authorG. N. KUROV, G. N. KUROVSearch for more papers by this authorG. G. SKVORTSOVA, G. G. SKVORTSOVASearch for more papers by this author First published: March 17, 1981 https://doi.org/10.1002/chin.198111269Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume12, Issue11March 17, 1981 RelatedInformation

The mechanism of electron transfer in laccase-catalysed reactions

1. 1. The reaction of the electron acceptors in Rhus vernicifera laccase (monophenol, dihydroxyphenylalanine:oxygen oxidoreductase, EC 1.14.18.1) have been studied with stopped-flow and rapid-freeze EPR techniques. The studies have been directed mainly towards elucidation of the role of the type 2 Cu 2+ as a possible pH-sensitive regulator of electron transfer. 2. 2. Anaerobic reduction experiments with Rhus laccase indicate that the type 1 and 2 sites contribute one electron each to the reduction of the two-electron-accepting type 3 site. There is also evidence that the reduction of the type 1 Cu 2+ triggers the reduction of the type 2 Cu 2+. 3. 3. Only at pH values at which the reduction of the two-electron acceptor is limited by a slow intramolecular reaction can an OH − be displaced from the type 2 Cu 2+ by the inhibitor F −. 4. 4. A model describing the role of the electron-accepting sites in catalysis is formulated.

Characterization of the extracellular, water-insoluble α- D-glucans of oral streptococci by methylation analysis, and by enzymic synthesis and degradation

Methylation analysis of water-insoluble α- D-glucans synthesized from sucrose by culture filtrates from several strains of Streptococcus spp. has proved that all of the glucans were highly branched and that the chains contained (1→6)- and (1→3)-linked D-glucose residues not involved in branch points. Hydrolysis of the glucans with a specific endo-(1→3)-α- D-glucanase demonstrated that the majority of the (1→3)-linked glucose residues were arranged in sequences. D-Glucose was the major product of the hydrolysis, and a small proportion of nigerose was also released. The use of a specific endo-(1→6)-α- D-glucanase similarly indicated that the glucans also contained sequences of (1→6)-linked α- D-glucose residues, and that those chains were branched. Two D-glucosyltransferases (GTF-S and GTF-I), which reacted with sucrose to synthesize a soluble glucan and a water-insoluble glucan, respectively, were separated from culture filtrates of S. mutans OMZ176. The soluble glucan was characterized as a branched (1→6)-α- D-glucan, whereas the insoluble one was a relatively linear (1→3)-α- D-glucan. The hypothesis is advanced that the glucosyltransferases can transfer glucan sequences by means of acceptor reactions similar to those proposed by Robyt for dextransucrase, leading to the synthesis of a highly branched glucan containing both types of chain. The resulting structure is consistent with the evidence obtained from methylation analysis and enzymic degradations, and explains the synergy displayed when the two D-glucosyltransferases interact with sucrose. Variations in one basic structure can account for the characteristics of water-insoluble glucans from S. sanguis and S. salivarius, and for the strain-dependent diversity of S. mutans glucans.