Acta chemica Scandinavica (Copenhagen, Denmark : 1989)最新文献

{"title":"Tyrosyl radicals in enzyme catalysis: some properties and a focus on photosynthetic water oxidation.","authors":"G T Babcock,&nbsp;M Espe,&nbsp;C Hoganson,&nbsp;N Lydakis-Simantiris,&nbsp;J McCracken,&nbsp;W Shi,&nbsp;S Styring,&nbsp;C Tommos,&nbsp;K Warncke","doi":"10.3891/acta.chem.scand.51-0533","DOIUrl":"https://doi.org/10.3891/acta.chem.scand.51-0533","url":null,"abstract":"<p><p>Enzymes that require a redox-active amino acid for catalysis or function have emerged as a distinct class of proteins. For the tyrosine-based radical enzymes, we show that the spin-density distribution in the radical follows an odd alternate pattern that is invariant to within 10% across the class. General properties of the radical enzymes are summarized from which we conclude that their essential role in catalysis is to initiate substrate metabolism by hydrogen-atom abstraction. These ideas are extended to the YZ and YD tyrosines in Photosystem II and a radical-based hydrogen-atom abstraction model for water oxidation is discussed. Differences in rates of oxidation of YZ and YD by the reaction-center chlorophyll, P680+, under various conditions, are considered and rationalized on the basis of changes in reorganization energy induced by the local protein structure and by the presence or absence of the (Mn)4 cluster that binds substrate water.</p>","PeriodicalId":76966,"journal":{"name":"Acta chemica Scandinavica (Copenhagen, Denmark : 1989)","volume":"51 5","pages":"533-40"},"PeriodicalIF":0.0,"publicationDate":"1997-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"20135728","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Interaction of MRI gadolinium contrast agents with phospholipid bilayers as studied by 95 GHz EPR.","authors":"T I Smirnova,&nbsp;A I Smirnov,&nbsp;R L Belford,&nbsp;R B Clarkson","doi":"10.3891/acta.chem.scand.51-0562","DOIUrl":"https://doi.org/10.3891/acta.chem.scand.51-0562","url":null,"abstract":"<p><p>Interactions of two MRI gadolinium contrast agents, gadolinium ethoxybenzyl-diethylenetriaminepentaacetate (Gd-EOB-DTPA) and gadolinium N-pentyl-1,4,7,10-tetraazacyclododecane-N',N\",N'\"- triacetic acid (Gd-DOTA-P), with multibilayer phospholipid dispersions prepared from 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) have been investigated with high resolution EPR spectroscopy at 95 GHz. At a resonance field of 3.3 T, EPR spectra of a small nitroxide probe, 2,2,6,6-tetramethyl-1-piperidinyloxyl (Tempo), partitioned between aqueous and membrane phases are clearly resolved, making measurements of dynamics parameters of the probe accurate and unambiguous. Results show that although the presence of the more lipophilic contrast agent, Gd-DOTA-P, can be detected within the bilayer, the structural organization of the membrane remains unaffected even at physiologically high (5 mM) concentrations. The temperature of the main phase transition of the bilayer was also unaffected to within the 0.4 degree C accuracy of its determination.</p>","PeriodicalId":76966,"journal":{"name":"Acta chemica Scandinavica (Copenhagen, Denmark : 1989)","volume":"51 5","pages":"562-6"},"PeriodicalIF":0.0,"publicationDate":"1997-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"20135619","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Attempt to solubilize Na+/K+-exchanging ATPase with amphiphilic peptide PD1.","authors":"U Soomets,&nbsp;C Kairane,&nbsp;M Zilmer,&nbsp;U Langel","doi":"10.3891/acta.chem.scand.51-0403","DOIUrl":"https://doi.org/10.3891/acta.chem.scand.51-0403","url":null,"abstract":"<p><p>The effect of the 24-amino-acid-long peptide, PD(1), on rat cerebral cortical Na+/K+ -exchanging ATPase (EC 3.6.1.37) has been studied. Incubation of the enzyme preparation (25 degrees C for 10-25 min) with the peptide (10(-7) - 10(-4) M) did not appreciably affect the activity of the enzyme, only 5-8% activation being registered. On the other hand, PD(1) completely eliminated the cooperative nature of Na+ -binding to Na+/K+ -exchanging ATPase (n(H) decreased from 1.4 to 0.9) and slightly (1.2-fold) decreased the affinity for Na+. ATP, a substrate of activity for Na+/K+ -exchanging ATPase, blocked the PD(1)-promoted effect on the cooperativity for Na+. Incubation of cerebral cortical membranes with 5 x 10(-4) M PD(1) revealed a shift (from 19.5 degrees C to 21.4 degrees C) of the typical break on the Arrhenius plot (15-37 degrees C). Prolonged incubation of enzyme preparation (25 degrees C for 1-2 h) with PD(1) (4.5 x 10(-4) - 0.7 x 10(-2) M) followed by centrifugation of the mixture at 53,000 g for 90 min, resulted in loss of the activity both in the supernatant and the sediment, while the protein content in the supernatant and the sediment remained unchanged. After a short incubation (25 degrees for 10 min) with PD(1) (1 x 10(-6) M), followed by centrifugation, the full activity of Na+/K+ -exchanging ATPase in the sediment was restored. These data suggest that peptitergent PD(1) does not solubilize the transmembrane protein Na+/K+ -exchanging ATPase, although it abolishes the cooperative effect of Na+.</p>","PeriodicalId":76966,"journal":{"name":"Acta chemica Scandinavica (Copenhagen, Denmark : 1989)","volume":"51 3 Suppl","pages":"403-6"},"PeriodicalIF":0.0,"publicationDate":"1997-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"20197398","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Anti-HIV active naphthyl analogues of HEPT and DABO.","authors":"K Danel,&nbsp;C Nielsen,&nbsp;E B Pedersen","doi":"10.3891/acta.chem.scand.51-0426","DOIUrl":"https://doi.org/10.3891/acta.chem.scand.51-0426","url":null,"abstract":"<p><p>5-Ethyl-6-(1-naphthylmethyl)uracil and 5-ethyl-6-(1-naphthylmethyl)-2-thiouracil were alkylated to give, respectively. N-1 and S2, ethoxymethyl and methylthiomethyl uracil derivatives. 5-Ethyl-6-(1-naphthylmethyl)-2-thiouracil was also S2 alkylated with methyl bromoacetate. The products showed activity against HIV-1, and the N-1 alkylated derivatives were indeed highly active.</p>","PeriodicalId":76966,"journal":{"name":"Acta chemica Scandinavica (Copenhagen, Denmark : 1989)","volume":"51 3 Suppl","pages":"426-30"},"PeriodicalIF":0.0,"publicationDate":"1997-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"20155383","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"EPR, ENDOR and TRIPLE resonance and MO studies on ubiquinones (Q-n): comparison of radical anions and cations of coenzymes Q-10 and Q-6 with the model compounds Q-2 and Q-0.","authors":"H Joela,&nbsp;S Kasa,&nbsp;P Lehtovuori,&nbsp;M Bech","doi":"10.3891/acta.chem.scand.51-0233","DOIUrl":"https://doi.org/10.3891/acta.chem.scand.51-0233","url":null,"abstract":"<p><p>Radical anions and cations of the biologically important coenzymes Q-6 and Q-10, which have 6 and 10 unsaturated isoprene units in their side chains, respectively, have been generated in various solvents, and the results compared with those obtained for Q-0, a ubiquinone with no isoprene units, and for decylubiquinone Q-2 which has a saturated side chain. Hyperfine splitting constants (hfsc) of methyl and methoxy protons of the substituents in the quinone ring, and beta and gamma protons of the side chain were measured by EPR and ENDOR spectroscopy for both the radical anions and cations of Q-0, Q-6 and Q-10, and for the radical anion of Q-2. The relative signs of the hfsc were determined by general TRIPLE resonance spectroscopy. TRIPLE induced EPR (TIE) spectra were used for identification of the primary and secondary radicals of Q-10. The temperature dependence of the hfsc of the beta protons of Q-2 was different from those of Q-6 and Q-10. Fully optimised structures of Q-3 and Q-7 were obtained by performing semiempirical PM3 molecular orbital (MO) calculations for both neutral molecules and radical anions, neutral radicals and radical cations. Partial optimisation of the molecules was carried out for the side chain in a planar conformation. The folded conformation always had the minimum energy. Folding was so complete in the Q-7 series that the end of the side chain came into contact with the quinone ring, and small hfsc were detected in the PM3 calculations.</p>","PeriodicalId":76966,"journal":{"name":"Acta chemica Scandinavica (Copenhagen, Denmark : 1989)","volume":"51 2","pages":"233-41"},"PeriodicalIF":0.0,"publicationDate":"1997-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"20017976","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Synthesis of diastereomeric mixtures of 5'-C-hydroxymethylthymidine and introduction of a novel class of C-hydroxymethyl functionalised oligodeoxynucleotides.","authors":"J Fensholdt,&nbsp;J Wengel","doi":"10.3891/acta.chem.scand.50-1157","DOIUrl":"https://doi.org/10.3891/acta.chem.scand.50-1157","url":null,"abstract":"<p><p>Novel 5'-C-hydroxymethyl substituted derivatives of thymidine have been prepared by dihydroxylation of the 5'C-methylene nucleoside 1. Osmium tetraoxide catalysed dihydroxylation of 1 afforded a 3:2 epimeric mixture of diols 2, whereas asymmetric dihydroxylation using AD-mix-alpha and AD-mix-beta resulted in mixtures 3 and 4 of the two epimeric diols, both enriched with the same diastereomer. Nucleosides 2 were transformed into phosphoramidites 8 which were used for solid phase synthesis of oligodeoxynucleotides (ODNs) containing 5'-C-(hydroxymethyl) functionalised thymidine monomers. This novel class of C-hydroxymethyl modified ODN-analogues exhibited promising affinity towards both complementary DNA and RNA as well as resistance towards 3'-exonucleolytic degradation.</p>","PeriodicalId":76966,"journal":{"name":"Acta chemica Scandinavica (Copenhagen, Denmark : 1989)","volume":"50 12","pages":"1157-63"},"PeriodicalIF":0.0,"publicationDate":"1996-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"19945708","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Solid phase synthesis of two phosphorylated peptides related to casein using allyl phosphate protection, and their CD spectra.","authors":"E Larsson,&nbsp;B Lüning,&nbsp;J Reed,&nbsp;C Krog-Jensen","doi":"10.3891/acta.chem.scand.50-1009","DOIUrl":"https://doi.org/10.3891/acta.chem.scand.50-1009","url":null,"abstract":"<p><p>Phosphoserine peptides related to the casein kinase II substrate consensus sequence ESLSSSEE have been synthesized using N-Boc-O-diallylphosphono-L-serine by solid-phase methods. The allyl groups were removed, while the peptide was still attached to the solid support, by Pd0 with azide as the nucleophile. Far UV circular dichroism measurements indicate that peptides phosphorylated at Ser 4 or Ser 5 have a somewhat higher content of ordered structure than the non-phosphorylated peptide.</p>","PeriodicalId":76966,"journal":{"name":"Acta chemica Scandinavica (Copenhagen, Denmark : 1989)","volume":"50 11","pages":"1009-12"},"PeriodicalIF":0.0,"publicationDate":"1996-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"19864941","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Synthesis of kojitriose using silicon-tethered glycosidation.","authors":"M Bols","doi":"10.3891/acta.chem.scand.50-0931","DOIUrl":"https://doi.org/10.3891/acta.chem.scand.50-0931","url":null,"abstract":"<p><p>Reaction of 3,4,6-tri-O-acetyl-beta-D-glucopyranosyl chloride (1) with potassium phenylselenate gave phenyl 3,4,6-tri-O-acetyl-1-seleno-alpha, beta-D-glucopyranoside (2) in 59% yield. Silylation of benzyl 3,4,6-tri-O-benzyl-beta-D-glucopyranoside (4) with ethyl 3,4,6-tri-O-benzyl-2-O-chlorodimethylsilyl-1-thio-beta -D-glucopyranoside gave benzyl 2-O-(3,4, 6-tri-O-benzyl-1-S-ethyl-1-thio-beta-D-glucopyranos-2-O-yldimet hylsilyl)-3,4,6,-tri-O-benzyl-beta-D-glucopyranoside (5) in 35% yield. Reaction of 5 with N-iodosuccinimide in nitromethane gave benzyl 2-O-(3,4, 6-tri-O-benzyl-alpha-D-glucopyranosyl)-3,4, 6-tri-O-benzyl-beta-D-glucopyranoside (6) in 45% yield. Chlorodimethylsilylation of phenyl 3,4, 6-tri-O-acetyl-1-seleno-alpha-D-glucopyranoside (2 alpha) and reaction with 6 gave benzyl 2-O-[2-O-(3,4,6 -tri-O-acetyl-1-Se-phenyl-1-seleno-alpha-D-glucopyranos-2-O-yld imethylsilyl) -3,4,6-tri-O-benzyl-alpha-D-glucopyranosyl]-3,4,6-tri-O-benzyl-beta-D- glucopyranoside (7) in 82% yield. Intramolecular glycosidation of 7 using N-iodosuccinimide in nitromethane gave benzyl 2-O-[2-O-(3,4,6-tri-O-acetyl-alpha-D-glucopyranosyl)-3, 4,6-tri-O-benzyl-alpha-D-glucopyranosyl]-3, 4,6-tri-O-benzyl-beta-D-glucopyranoside (8) in 45% yield. Deprotection of 8 gave kojitriose (9) in quantitative yield. Chlorodimethylsilylation of 1,3,4,6-tetra-O-benzyl-alpha, beta-D-fructofuranose (10) with dimethyldichlorosilane and pyridine followed by reaction with ethyl 3,4, 6-tri-O-benzyl-1-thio-beta-D-glucopyranoside (3) gave ethyl 2-O-(1,3,4,6-tetra-O-benzyl-alpha, beta-D-fructofuranosyloxydimethylsilyl)-3,4, 6-tri-O-benzyl-1-thio-beta-D-glucopyranoside (11) in 85% yield. Chlorodimethylsilylation of 1,3,4, 6-tetra-O-benzoyl-alpha-D-fructofuranose (12) with dimethyldicholorosilane and triethylamine followed by reaction with phenyl 3,4, 6-tri-O-acetyl-1-thio-alpha-D-glucopyranoside (13) gave phenyl 2-O-(1,3,4, 6-tetra-O-benzoyl-alpha-D-fructofuranosyloxydimethylsilyl)-3, 4,6-tri-O-acetyl-1-thio-alpha-D-glucopyranoside (14) in 62% yield. Both 11 and 14 failed to undergo intramolecular glycosidation.</p>","PeriodicalId":76966,"journal":{"name":"Acta chemica Scandinavica (Copenhagen, Denmark : 1989)","volume":"50 10","pages":"931-7"},"PeriodicalIF":0.0,"publicationDate":"1996-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"19848690","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Neothyoside B, a triterpenoid diglycoside from the Pacific sea cucumber Neothyone gibbosa.","authors":"R Encarnación,&nbsp;J I Murillo,&nbsp;J Nielsen,&nbsp;C Christophersen","doi":"10.3891/acta.chem.scand.50-0848","DOIUrl":"https://doi.org/10.3891/acta.chem.scand.50-0848","url":null,"abstract":"","PeriodicalId":76966,"journal":{"name":"Acta chemica Scandinavica (Copenhagen, Denmark : 1989)","volume":"50 9","pages":"848-9"},"PeriodicalIF":0.0,"publicationDate":"1996-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"19785824","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Cation-dependent interactions of calreticulin with denatured and native proteins.","authors":"C Wiuff,&nbsp;G Houen","doi":"10.3891/acta.chem.scand.50-0788","DOIUrl":"https://doi.org/10.3891/acta.chem.scand.50-0788","url":null,"abstract":"Calreticulin has sequence homology with the molecular chaperone calnexin, which is known to control folding and assembly of nascent proteins in the endoplasmic reticulum in a calcium-dependent manner. We have investigated the interaction between human placental calreticulin and denatured placental and serum proteins under various incubation conditions. The interactions with denatured proteins differed significantly from the interactions with native proteins. The interactions were highly dependent on divalent metal ions or polyamines, but were not influenced by detergent and sulfhydryl agents. Our results indicate that calreticulin might have a similar role in protein folding as the chaperone calnexin.","PeriodicalId":76966,"journal":{"name":"Acta chemica Scandinavica (Copenhagen, Denmark : 1989)","volume":"50 9","pages":"788-95"},"PeriodicalIF":0.0,"publicationDate":"1996-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"19785823","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}