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Marked Preference (marked + preference)
Selected AbstractsTransgalactosylation by thermostable ,-glycosidases from Pyrococcus furiosus and Sulfolobus solfataricusFEBS JOURNAL, Issue 16 2000-glycosides during lactose conversion, Binding interactions of nucleophiles with the galactosylated enzyme intermediate make major contributions to the formation of new The hyperthermostable ,-glycosidases from the Archaea Sulfolobus solfataricus (Ss,Gly) and Pyrococcus furiosus (CelB) hydrolyse ,-glycosides of d -glucose or d -galactose with relaxed specificities pertaining to the nature of the leaving group and the glycosidic linkage. To determine how specificity is manifested under conditions of kinetically controlled transgalactosylation, the major transfer products formed during the hydrolysis of lactose by these enzymes have been identified, and their appearance and degradation have been determined in dependence of the degree of substrate conversion. CelB and Ss,Gly show a marked preference for making new ,(1,3) and ,(1,6) glycosidic bonds by intermolecular as well as intramolecular transfer reactions. The intramolecular galactosyl transfer of CelB, relative to glycosidic-bond cleavage and release of glucose, is about 2.2 times that of Ss,Gly and yields ,- d -Galp- (1,6)- d -Glc and ,- d -Galp- (1,3)- d -Glc in a molar ratio of ,,1 : 2. The partitioning of galactosylated Ss,Gly between reaction with sugars [kNu (m,1·s,1)] and reaction with water [kwater (s,1)] is about twice that of CelB. It gives a mixture of linear ,- d -glycosides, chiefly trisaccharides at early reaction times, in which the prevailing new glycosidic bonds are ,(1,6) and ,(1,3) for the reactions catalysed by Ss,Gly and CelB, respectively. The accumulation of ,- d -Galp- (1,6)- d -Glc at the end of lactose hydrolysis reflects a 3,10-fold specificity of both enzymes for the hydrolysis of ,(1,3) over ,(1,6) linked glucosides. Galactosyl transfer from Ss,Gly or CelB to d -glucose occurs with partitioning ratios, kNu/kwater, which are seven and >,170 times those for the reactions of the galactosylated enzymes with 1-propanol and 2-propanol, respectively. Therefore, the binding interactions with nucleophiles contribute chiefly to formation of new ,-glycosides during lactose conversion. Likewise, noncovalent interactions with the glucose leaving group govern the catalytic efficiencies for the hydrolysis of lactose by both enzymes. They are almost fully expressed in the rate-limiting first-order rate constant for the galactosyl transfer from the substrate to the enzyme and lead to a positive deviation by ,,2.5 log10 units from structure,reactivity correlations based on the pKa of the leaving group. [source] Ovipositional discrimination by Microplitis rufiventris females between healthy and granulosis virus-infected Spodoptera littoralis larvaeJOURNAL OF APPLIED ENTOMOLOGY, Issue 1 2004E. M. Hegazi Abstract: Ovipositional choice tests by Microplitis rufiventris females (Hym., Braconidae) between granulosis virus-infected (GVI) and non-infected (NI) Spodoptera littoralis larvae (Lep., Noctuidae), were assessed using discriminatory methods for re-isolating the NI and virus-infected hosts after removing the female parasitoid. When M. rufiventris females were given a choice between NI and GVI S. littoralis hosts, the adult females exhibited marked preference (P < 0.01) for the NI (i.e. higher quality) hosts. In this case, M. rufiventris females and S. littoralis GV (SlGV) did not significantly compete for the same type of host larvae and are, generally, compatible. However, when the choice was given between two low qualities of S. littoralis hosts, i.e. virus-free previously parasitized hosts and viral-infected hosts a significant preference (P < 0.01) of the parasitoid females for the GVI larvae was observed. In this case, the parasitoid would be at a disadvantage when competing with GV for the same host. However, the parasitoid could be used as an additional tool for the dissemination of biocontrol viruses within different pest populations, i.e. hosts other than S. littoralis. Importantly, the results showed different strategies of parasitoid female in egg-laying management. When M. rufiventris female was given a choice between healthy and SlGVI hosts, the female deposited more eggs than when she was given a choice between two low qualities of host larvae. The results of the study may have implications in pest management strategies using M. rufiventris and SlGV against S. littoralis larvae. [source] Spatial and temporal dynamics of Myzus persicae clones in fields and suction trapsAGRICULTURAL AND FOREST ENTOMOLOGY, Issue 2 2008Louise Kasprowicz Abstract 1,The population of peach-potato aphid Myzus persicae in Scotland is comprised almost entirely of long-term asexual clones. 2,Over a ten year period, M. persicae from Scottish fields and suction traps were analysed with six microsatellite markers. 3,Out of 1497 individuals analysed, 14 clones (denoted A,N) comprised over 98% of the collection. 4,Some clones were particularly abundant but most clones had a widespread distribution on all available plants. 5,Clones E and L had distinct features in their distributions as clone L was geographically totally restricted to the north east of Scotland and clone E showed a marked preference for brassica crops. 6,Clones E and L provide direct evidence of a role for local adaptations in the distribution of M. persicae clones. [source] Study of the conformational profile of the norbornane analogues of phenylalanineJOURNAL OF PEPTIDE SCIENCE, Issue 6 2002Arnau Cordomí Abstract The conformational profile of the eight stereoisomeric 2-amino-3-phenylnorbornane-2-carboxylic acids (2-amino-3-phenylbicyclo[2.2.1]heptane-2-carboxylic acids) has been assessed by computational methods. These molecules constitute a series of four enantiomeric pairs that can be considered as rigid analogues of either L - or D -phenylalanine. The conformational space of their N -acetyl methylamide derivatives has been explored within the molecular mechanics framework, using the parm94 set of parameters of the AMBER force field. Local minimum energy conformations have been further investigated at the ab initio level by means of the Hartree-Fock and second order Moller-Plesset perturbation energy calculations using a 6,31G(d) basis set. The results of the present work suggest that the bulky norbornane structure induces two kinds of conformational constraints on the residues. On one hand, those of a steric nature directly imposed by the bicycle on the peptide backbone and, on the other hand, those that limit the orientations attainable by the phenyl ring which, in turn, reduces further the flexibility of the peptide backbone. A comparative analysis of the conformational profile of the phenylnorbornane amino acids with that of the norbornane amino acids devoid of the ,-phenyl substituent suggests that the norbornane system hampers the residue to adopt extended conformations in favour of C7-like structures. However, the bicycle itself does not impart a clear preference for any of the two possible C7 minima. It is the aromatic side chain, which is forced to adopt an almost eclipsed orientation, that breaks this symmetry introducing a marked preference for a single region of the (,, ,) conformational space in each of the phenylalanine norbornane analogues investigated. Copyright © 2002 European Peptide Society and John Wiley & Sons, Ltd. [source] Effects of Long-Term Episodic Access to Ethanol on the Expression of an Alcohol Deprivation Effect in Low Alcohol,Consuming RatsALCOHOLISM, Issue 12 2004Richard L. Bell Background: The alcohol-preferring (P) and -nonpreferring (NP) and high alcohol,drinking (HAD) and low alcohol,drinking (LAD) rats have been selectively bred for divergent preference for ethanol over water. In addition, both P and HAD rats display an alcohol deprivation effect (ADE). This study was undertaken to test whether the NP, LAD-1, and LAD-2 lines of rats could display an ADE as well. Method: Adult female NP, LAD-1, and LAD-2 rats were given concurrent access to multiple concentrations of ethanol [5, 10, 15% (v/v)] and water in an ADE paradigm involving an initial 6 weeks of 24-hr access to ethanol, followed by four cycles of 2 weeks of deprivation from and 2 weeks of re-exposure to ethanol (5, 10, and 15%). A control group had continuous access to the ethanol concentrations (5, 10, and 15%) and water through the end of the fourth re-exposure period. Results: For NP rats, a preference for the highest ethanol concentration (15%) was evident by the end of the fifth week of access (,60% of total ethanol fluid intake). Contrarily, LAD rats did not display a marked preference for any one concentration of ethanol. All three lines displayed an ADE after repeated cycles of re-exposure to ethanol, with the general ranking of intake being LAD-1 > NP > LAD-2 (e.g., for the first day of reinstatement of the third re-exposure cycle, intakes were 6.5, 2.9, and 2.4 g/kg/day compared with baseline values of 3.1, 2.0, and 1.3 g/kg/day for each line, respectively). By the 13th week, rats from all three lines, with a ranking of LAD-1 > NP > LAD-2, were drinking more ethanol (3.3, 2.2, and 2.0 g/kg/day, respectively) compared with their consumption during the first week of access (,1.1 g/kg/day for all three lines). Conclusion: These data indicate that access to multiple concentrations of ethanol and exposure to multiple deprivation cycles can partially overcome a genetic predisposition of NP, LAD-1, and LAD-2 rats for low alcohol consumption. In addition, the findings suggest that genetic control of low alcohol consumption in rats is not associated with the inability to display an ADE. [source] The S2 subsites of cathepsins K and L and their contribution to collagen degradationPROTEIN SCIENCE, Issue 4 2007Fabien Lecaille Abstract The exchange of residues 67 and 205 of the S2 pocket of human cysteine cathepsins K and L induces a permutation of their substrate specificity toward fluorogenic peptide substrates. While the cathepsin L-like cathepsin K (Tyr67Leu/Leu205Ala) mutant has a marked preference for Phe, the Leu67Tyr/Ala205Leu cathepsin L variant shows an effective cathepsin K-like preference for Leu and Pro. A similar turnaround of inhibition was observed by using specific inhibitors of cathepsin K [1-(N -Benzyloxycarbonyl-leucyl)-5-(N -Boc-phenylalanyl-leucyl)carbohydrazide] and cathepsin L [N -(4-biphenylacetyl)- S -methylcysteine-(D)-Arg-Phe-,-phenethylamide]. Molecular modeling studies indicated that mutations alter the character of both S2 and S3 subsites, while docking calculations were consistent with kinetics data. The cathepsin K-like cathepsin L was unable to mimic the collagen-degrading activity of cathepsin K against collagens I and II, DQ-collagens I and IV, and elastin-Congo Red. In summary, double mutations of the S2 pocket of cathepsins K (Y67L/L205A) and L (L67Y/A205L) induce a switch of their enzymatic specificity toward small selective inhibitors and peptidyl substrates, confirming the key role of residues 67 and 205. However, mutations in the S2 subsite pocket of cathepsin L alone without engineering of binding sites to chondroitin sulfate are not sufficient to generate a cathepsin K-like collagenase, emphasizing the pivotal role of the complex formation between glycosaminoglycans and cathepsin K for its unique collagenolytic activity. [source] | ||||||||||