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1.
The previously introduced conceptual parameters (, , and S)to describe the stereochemical requirements for organic compoundsto taste sweet, were now applied to another series of sweetenersand to some well-known potent substances. With the help of anadapted STERIMOL computer program, the positions of relevant,hydrophobic side chains were determined in ureas, saccharins,tryptophans, chlorosugars and acesulfame derivatives in relationto their AH-B moieties. The results obtained were compared withprevious findings for five other homologous series of sweeteners.There is evidence to suggest that 6-substituted acesulfame derivativesand saccharin employ the same receptor site. in 5-substitutedacesulfame derivatives coincides with that of sulphamates calculatedearlier. in 6-chloro-D-tryptophan was found to be at equaldistances from H and B, a position which was earlier also observedfor the methyl ester group in aspartame. In the dulcin seriesof the urea derivatives, two AH-B moieties can be distinguished:the HN-CO group gives rise to , and 's which fit in the earliercalculated nitroaniline receptor site, while for the OC-NH2group they are located near those found for isocoumarins. Thechlorine atoms in 1' '16'-dichlorosucrose are located aboveand below the plane of the pyranose ring at almost the samepositions with respect to the OH groups at positions 3 and 4(in fact, two equal 's), which are supposed to form the AH-Bmoiety. The high relative sweetness values of 1',6'-dichlorosucroseand 1',4,6'-trichlorogalactosucrose are most probably due tothe fact that both sweeteners can interact with the receptorsite in two ways (as such and upside-down). It is remarkablethat the average positions belonging to sweeteners with similarAH-B moieties are located very close to each other.  相似文献   

2.
The olfactory-mediated responses to the sex hormone 17,20ß-dihydroxy-4-pregnen-3-one(17,20ß-P) were studied in spermiated and regressedmale crucian carp (Carassius carassius L). The position andspontaneous locomotor activity of single male crucian carp werecontinuously recorded in an artificial stream. 17,20ß-P(final concentration 10–11 M) was supplied to one halfand its ethanol carrier to the other half of the test area.Milt volume and gonadotropin (GtH-II) concentration in the plasmawere also measured. The smell of 17, 20ß-P significantlyincreased both the GtH-II concentration in the plasma and thevolume of strippable milt in spermiated crucian carp. Behaviorally,the side of the test area scented with 17,20ß-P wassignificantly avoided by spermiated males. None of the describedeffects of 17,20ß-P on spermiated males were observedfor the regressed crucian carp. In view of the lack of responsefrom regressed crucian carp we suggest that the observed avoidancebehavior of 17,20ß-P by spermiated males is a relevantreaction for spawning male crucian carp. The results are wellin accordance with responses obtained in the closely relatedgoldfish and gives strong support that the wild male cruciancarp use the 17,20ß-P signal from the females to preparefor the coming spawning.  相似文献   

3.
Methyl--D-mannopyranoside is a glycoside with a bitter-sweettaste. Adaptation to sucrose reduces the sweetness and adaptationto quinine sulphate reduces the bitterness of methyl--Dmannopyranoside.Application of Gymnema sylvestre reduces the sweetness of methyl--D-mannopyranosidewithout reducing its bitterness. These results, predicted byprevious studies, contradict a recent hypothesis and reportby Birch and Mylvaganam. 1Supported by NIH Grant 2-RO1-NS07873-9  相似文献   

4.
Besides the hydrophilic AH-B moiety in sweeteners, the morehydrophobic ‘third binding sites’ play an essentialrole in inducing sweetness. The distances between these molecularfunctions seem to be very critical, but exact data are lacking.To describe stereochemical requirements more precisely, newconceptual parameters were introduced, namely , and (minimum,optimum and maximum distances between these third binding sitesand the atoms A, H and B of the AH-B moieties respectively,especially appropriate for homologous series) and the S value(shortest distance between the position of an atom and the planeformed by the atoms A, H and B of the AH-B moiety). The dimensionsof the relevant side chains of five homologous series of sweeteners– sulphamates, oximes, nitroanilines, isocoumarins anddipeptides — were determined. We calculated that the positionsof the , and parameters with regard to the AH-B moieties arelocated around two main axes forming 95? angles with the H-Baxis in the AH-B moieties for sulphamates and isocoumarins and125? angles for oximes, nitroanilines and dipeptides. The positionsof are, for all potent sweeteners, situated at 70—85%of the maximum distance of viewed from the centre of the Aatom, while for , this value was found to be 15% for oximes,25% for nitroanilines, 40% for sulphamates, 50—70% fordipeptides and 65% for isocoumarins. The results indicate thereare at least three — but a maximum of four — differentreceptor sites. They have very narrow site clefts with maximumheights of -0.6 nm.  相似文献   

5.
6.
The glycoside methyl 4,6-dichloro–4,6-dideoxy--D-galactopyranoside,an inhibitor of electrophysiological responses to sweet tastein gerbils, was also found to suppress the perceived intensitiesof various sweeteners in human psychophysical experiments. Incontrast, this compound did not suppress the salty and sourtastes in either species.  相似文献   

7.
Tekin  A.R.; Karaman  H. 《Chemical senses》1992,17(6):795-799
The olfactory threshold concentrations of 19 derivatives ofethyl ß-methyl-ß-phenyl-,ß-epoxypropionate(strawberry aldehyde) were determined in water solution usinguntrained panellists. In spite of their similar carbon skeletons,the compounds differed considerably in their odor thresholdvalues. The lowest and highest values were found to be 0.5 p.p.m.(0.5 parts of the odorant per 106 parts of water) for ß-(bromophenyl)-,ß-epoxypropionateand 720 p.p.m. for n-octyl-,ß-epoxy propionate, respectively.  相似文献   

8.
nAlkyl - and -lactosides, galactosides and glucosides with differentalkyl chain lengths (C2, C8, C14, and C20) were synthesizedand used as acceptors for sialyltransferases from rat liverGolgi vesicles. The -galactosides, -glucosides, and both - and-lactosides, were sialylated. Keeping the acceptor concentrationconstant, sialylation rates reached a maximum for the n-octyl- and -lactosides, n-Octyl -galactoside and noctyl -glucoside,respectively. noctyl -glucoside, respectivwly. n-Octyl -galactosideand n-octyl -glucoside were not sialylated. The reaction productswere characterized by TLC. With n-octyl lactoside and galactosideas acceptors, two major sialylation products were formed. Thjeycould be separated by preparative TLC, and their structureswere identified as 2–3 and 2–6 sialylated acceptors,respectively, by a combination of periodated oxidation, NaBD4reduction,permethylation and subsequent analysis by fast atombombardment mass spectrometry (FAB-MS). The structure of thesingle product obtained from n-ictyl -glucoside was determinedto be the 2–6 sialylated glucoside. Competition experimentswith n-octyl lactoside and lactosylceramide and gangliosideGal1-3GalNAc1-4(NeuAc2–3)Gal1–4Glcbeeta1–1Cer(GM1) as acceptors for sialyltransferases suggested that SAT-I[NeuAc2–3Gal1–4Glc1-1Cer (GM3) synthase] was atleast in least in part responsible for the 2–3 sialylationof n-octyl lactoside. alkylgalactosides alkylglucosides alkyllactosides neoglycolipids sialytransferases  相似文献   

9.
A series of hydrophobic mannosides were synthesized and testedfor their ability to act as acceptor substrates for mannosyltransferasesin a Trypanosoma brucei cell-free system. The thiooctyl -mannosidesand octyl -mannosides all accepted single mannose residues in-linkage, as judged by thin layer chromatography of the productsbefore and after jack bean -mannosidase digestion. The mannosylationreactions were inhibited by amphomycin, suggesting that theimmediate donor was dolicholphosphate-mannose (Dol-P-Man) inall cases. The transferred -mannose residues were shown to beboth 1-2 and 1-6 linked by Aspergillus phoenicis -mannosidaseand acetolysis treatments, respectively. These data suggestthat the compounds can act as acceptor substrates for the Dol-P-Mandependent 1-2 and 1-6 mannosyltransferases of the GPI biosyntheticpathway and/or the dolichol-cycle of protein N-glycosylation.One of the compounds, Man1-6Man1-O-(CH2)7CH3, inhibited endogenousGPI biosynthesis in the cell-free system, suggesting that itcould be a substrate for the trypanosome Dol-P-Man:Man2GlcN-Pl1-2 mannosyltransferase. dolichol glycosylphosphatidylinositol mannosyltransferase trypanosome  相似文献   

10.
Information on the biological activities of gibberellins (GAs)in the barley aleurone, Tangin-bozu dwarf rice, dwarf pea, lettucehypocotyl and cucumber hypocotyl bioassays is reviewed and discussedin the context of GA structure-activity relationships. The barley aleurone bioassay exhibits a limited response toGAs and it is suggested that this may be because the aleuronecells are able to carry out few GA interconversions. Consequentlyactivity is determined by the degree of compatibility betweenthe GAs and a receptor site. In this assay high biological activityis associated with GAs having a 3ß-hydroxy--lactonestructure. This activity is substantially enhanced by the additionalpresence of a 13-hydroxyl group. The substitution of a -lactoneor a -lactol for a -lactone results in reduced activity while3ß,13-dihydroxy GAs with either 20-carboxyl or 20-methylfunctions are completely inactive. The Tanginbozu dwarf ricebioassay responds to many more GAs than the barley aleuronesystem possibly because the rice seedlings can carry out extensiveGA interconversions. Under these circumstances GAs that areinactive per se can be metabolically converted to active forms.There is no interaction between the 3ß- and 13-hydroxyfunctions of GA molecules in the rice assay. Activity appearsto be determined by the degree oxidation of the C-20 group.The order of activity is usually -lactone > -lactol >-lactone > methyl > carboxyl. It is suggested this mayindicate that in rice seedlings C20-GAs are converted to C19-GAsvia a Baeyer-Villiger type oxidation. Activity in the dwarfpea bioassay is dependent upon GAs possessing both 3ß-and 13-hydroxyl groups and is again related to the state ofoxidation at the C-20 locus. In the lettuce bioassay activityis restricted to GAs with a -lactone function. In some instancesa -lactone, but not a -lactol, can substitute effectively. Thismay imply that the applied C20-GAs are not converted to C19-GAsand that the response to the -lactone results from the six-memberedring mimicking the -lactone at the receptor site. Only GAs havinga 19,10 or a 19,20 lactonic bridge show substantial activityin the cucumber bioassay. The additional presence of eithera 12- or a 13-hydroxyl group severely reduces activity.  相似文献   

11.
Subunits (, ß, ) and mixtures of subunits ( ß, , ß , ß ) were isolated without denaturationfrom a chloroform extract of chloroplast coupling factor 1 (CF1)from maize (Zea mays var. Ushiku 5-4) and from spinach by fastprotein liquid chromatography (FPLC), on an anion-exchange columnof Mono-Q in the presence of n-octylglucoside (OG) and on achromatofocusing column of Mono-P. The ß -subunitcomplex (CF1 ß ) was the minimum unit required forATPase activity, as was confirmed by the reconstituted complexof ß and subunits. An subunit isolated from maizeinhibited the ATPase activity of CF1 ß from bothmaize and spinach. CF1 ß was found to contain anOG-dependent Mg2+-ATPase. The ATPase activity of CF1 ß required divalent cations, such as Mg2+ or Mn2+, for its expressionin the presence of OG; its optimum pH was 8.0 and it was markedlyinhibited by NaN3. The enzyme hydrolyzed ATP in prefernece toGTP but not CTP, UTP, ADP, AMP or pNPP. Lineweaver-Burk plotsof its activity were curvilinear in the range of 0.6–0.7mM ATP.Mg2+. 1Present address: Department of Biology, School of Education,Waseda University, Shinjuku-ku, Tokyo, 160 Japan. (Received February 15, 1989; Accepted April 20, 1989)  相似文献   

12.
The effects of -hydroxy-2-pyridinemethanesulphonic acid (-HPMS)upon net photosynthesis (Pn, the CO2 compensation point (),post-lower illumination burst of CO2 (PLIB) and post-lower temperatureburst of CO2 (PLTB) in detached rye (Secale cereale L.) leaveswere investigated. At low concentrations ( 0.5 mol m–3),-HPMS initially stimulated Pn and decreased the magnitude ofboth PLIB and PLTB. The decreased at all concentrations of-HPMS (0.05–5.0 mol m–3. The effects of -HPMS onPn and were time-dependent and, after a few minutes, the Pnwas inhibited while values increased considerably. At a higherconcentration (5.0 mol m –3), the transient effects of-HPMS were shorter () or not observed at all (Pn. Both PLIBand PLTB, when expressed in relation to Pn, increased at higherlevels of this compound. Similar data with respect to the effectsof -HPMS on PLIB and PLTB were found for leaves of dandelion(Taraxacum officinale L.). The results suggest that -HPMS may stimulate Pn by inhibitingphotorespiration, as originally suggested by Zelitch (1966),but only at low concentrations and over a short time span. Thedecrease of PLIB and PLTB values at low -HPMS levels is consistentwith these processes being a residual activity of the glycolatepathway. Key words: CO2 compensation point, -hydroxy-2-pyridinemethanesulphonic acid, photorespiration, photosynthesis  相似文献   

13.
The 1,2-fucosyltransferase family (1,2FT) is the largest familyof glycosyltransferases in the genome of the free-living nematodeCaenorhabditis elegans, and early evidence suggests that eachmember may have a unique activity. Here we describe a C. elegansgene (designated CE2FT-2) encoding an 1,2FT that has the potentialto generate the sequence Fuc1-2Galβ1-3GalNAc-R, which isthe H-type 3 blood group structure. The CE2FT-2 cDNA encodesa putative transmembrane protein that shows 42% amino acid identityto a previously cloned C. elegans 1,2FT (termed CE2FT-1), buthas a very low identity (16–20%) to 1,2FT sequences inhumans, rabbits, and mice. A recombinant form of CE2FT-2 expressedin human 293T cells has a high 1,2FT activity toward Galβ1-3GalNAc-O-pNP,but unexpectedly, the enzyme is inactive toward the acceptorGalβ-O-phenyl. Thus, CE2FT-2 differs from all other 1,2FTspreviously described from animals that all utilize Galβ-O-phenyl.CE2FT-2 is expressed at all stages of worm development, butremarkably, promoter analysis of the CE2FT-2 gene using greenfluorescent protein reporter constructs indicates that the CE2FT-2is expressed exclusively in pharyngeal cells of the worm fromembryo to an adult stage. Because pharyngeal cells are knownto secrete their glycoconjugates to the nematode surface, theseresults may indicate that products of CE2FT-2 contribute tointeractions of the nematode with its environment or are usedas ligands for bacterial attachment. These findings, along withthose on other 1,2FTs in C. elegans, suggest that each 1,2FTin this organism may have a unique acceptor specificity, expressionpattern, and biological function.  相似文献   

14.
The sexual agglutinability of haploid cells of heterothallicSaccharomyces cerevisiae was repressed when they were culturedin the absence of easily fermentable sugars, such as glucoseand mannose. The repression was reversed by the action of hormone-likesubstances of the opposite mating types. The substance producedby mating type cells was identical to subtsance-I which isknown to induce sexual agglutinability of inducible matingtype cells. The mating type cells produce a new hormone-likesubstance which induces or enhances sexual agglutinability of mating type cells. A crude fraction of the mating type-specific substance ( substance-I)was obtained by passing the culture filtrate of mating typecells through Amberlite CG-50 (H+ form), followed by elutionwith 1.5 M ammonia. 2 On leave from Osaka City University. (Received December 25, 1975; )  相似文献   

15.
The conformation of the heptasaccharide Man-1,6-(Man-1,3)(Xyl-ß1,2)-Man-ß,4-GlcNAc2-ß1,4-(L-Fuc-1,3)-GlcNAc1,the carbohydrate moiety of Erythrina corallodendron lectin (EcorL),the hexasaccharide Man-1,6-(Man-1,3) (GlcNAc-ß1,4)-Man-ß1,4-GlcNAc-ß1,4-GlcNAcand their disaccharide fragments have been studied by moleculardynamics (MD) simulations for 1000 ps with different initialconformations. In the isolated heptasaccharide, the most frequentlyaccessed conformation during MD has a value of 180° aroundMan-1,6-Man linkage. This conformation is stabilized by theformation of a hydrogen bond between the carbonyl oxygen ofGlcNAc2 with the O3/O4 hydroxyls of the 1,6-linked mannose residue.The conformation of the heptasaccharide found in the crystalstructure of the EcorL-lactose complex (Shaanan et al., Science,254, 862, 1991), that has a value of 76° around Man-1,6-Manlinkage, is accessed, although less frequently, during MD ofthe isolated oligosaccharide. The ,, = 58°,–134°,–60°conformation around Man-1,6-Man fragment observed in the crystalstructure of the Lathyrus ochnrs lectin complexed with a biantennaryoctasaccharide (Table I in Homans,S.W., Glycobiology, 3, 551,1993) has also been accessed in the present MD simulations.These values for the 1,6-linkage, which are observed in theprotein-carbohydrate crystal structures and are accessed inthe MD simulations, though occasionally, have not been predictedfrom NMR studies. Furthermore, these different values of leadto significantly different orientations of the 1,6-arm for thesame value of . This contrasts with the earlier predictionsthat only different values of can bring about significant changesin the orientation of the 1,6-arm. The MD simulations also showthat the effects of bisecting GlcNAc or ß1,2-xyloseare very similar on the 1,3-arm and slightly different on the1,6-arm. bisecting GlcNAc carbohydrates glycoprotein lectinsaccharide complex  相似文献   

16.
Enzymatic Degradation of Chlorophyll in Chenopodium album   总被引:3,自引:0,他引:3  
The breakdown of chlorophyll (Chi) in crude extracts of Chenopodiumalbum (white goose foot) in the dark was examined. Derivativesof pheophorbide were formed when Chi or chlorophyllide wasincubated with depigmented crude extracts. The formation ofpheophorbide was completely prevented by heat treatment of extracts,indicating that the reaction was enzymatic, and the presenceof a Mg-releasing enzyme, the so called Mg-dechelatase, waspostulated. This hypothesis was strongly supported by the observationthat the formation of pheophorbide was inhibited by 51% by 10mM MgCl2. Analysis by high-performance thin-layer chromatography(HPTLC) and liquid chromatography (HPLC) showed that the appearanceof chlorophyllide , pheophorbide 132-hydroxychlorophyllide and pyropheophorbide was accompanied by a concomitant decreasein levels of Chi The formation of 132-hydroxychloro-phyllide was not clearly an enzymatic reaction and requires furtherexamination. It appears that Chl is degraded in a crude extractof C. album via the following enzymatically catalyzed reactions (Received September 10, 1990; Accepted November 15, 1990)  相似文献   

17.
A Ras-related NTP-binding protein was partially purified froma membrane fraction derived from the mycelia of Neurospora crassa.[-32P]ATP and [-32P]GTP were incubated with mem brane and solublefractions which were then irradiated with UV light to inducecrosslinking of tightly bound nucleotides. After SDS-polyacrylamidegel electrophoresis, blotting onto a nitrocellulose filter andautoradiography it was apparent that most of the proteins thatbound [-32P]-GTP also bound [-32P]ATP. Pretreatment of the membranefraction with Ras-specific antibody effectively blocked thebinding of [-32P]ATP and [-32P]GTP to several ATP-GTP-bindingproteins. The band of a protein with a molecular weight of 26kDa on the SDS-polyacrylamide gel cross-reacted strongly withthe Ras-specific antibody. The protein was extracted from thegel and further purified by repeated gel electrophoresis. Thepurified protein bound [-32P]ATP, [-32P]-GTP, [-32P]CTP and[-32P]UTP at 1.6x10 M and was autophosphorylated in thepresence of [-32P]ATP and [-32P]GTP at 1.7x10 M. Pretreatmentof the protein with Ras-specific antibody partially blockedthe autophosphorylation in the presence of these nucleotides.The binding of [-32P]ATP to the NTP-binding protein was blockedby addition of ATP at 10–4–10–3 M. ATP ata concentration of 10–4 M prevented the binding of [-32P]to a greater extent than did GTP at the same concentration.Binding of [-32P]CTP and [-32P]UTP to the protein was also observed. (Received October 7, 1991; Accepted July 14, 1992)  相似文献   

18.
We cloned a Bacillus subtilis gene (srb) encoding a homologueof the mammalian signal recognition particle receptor -subunit(SR). The gene is 987 bp in length and encodes a 329-amino acidprotein. The deduced amino acid sequence of the protein shared26.6, 36.2 and 49.7% identity with those of mammalian SR, archaebacterialDP and Escherichia coli FtsY, respectively. The protein containsthree conserved GTP-binding elements like the other three SRPreceptor proteins, though the N-terminal portion of the putativeB. subtilis protein was shorter than the others. Secondary structureprediction showed that an amphipathic -helix is positioned inthe N-terminal region. A defect in srb inhibited cell growthand protein translocation.  相似文献   

19.
Fidgeon, C. and Wilson, G. 1988. Uptake and accumulation ofa-naphthalene acetic acid by cell suspensions of Galium mollugoL.—J. exp. Bot. 39: 241-249. Galium mollugo cell suspensions require -NAA for continued growthand cell division. The kinetics of -NAA uptake from the medium(B5) by Galium cells was assessed using 1-14C -NAA in a standardratio of cells to medium (0.25 g: 2.5 cm3). It was found thatthe uptake of -NAA was rapid, over 90% being taken up within4 h. Cells which had accumulated -NAA for 4 h or more did notrelease it back into the medium. It was found that Galium cellsaccumulated -NAA against a significant concentration gradient;suggesting the participation of an active component in the uptakemechanism. The effect of free-space and surface adsorption onthe uptake of -NAA was determined by means of a repeated washtechnique. These two factors were found to be of importanceonly during the first hour of uptake. Neither dead cells norplasmolysed cells absorbed -NAA. It is clear that, in the normal growth cycle, Galium cells cantake up the available -NAA within 3 or 4 h of inoculation andthat this can stimulate a cell division response of 3-4 generationsover the subsequent 14 d. Key words: Galium, cell suspension, -naphthalene acetic acid  相似文献   

20.
Previous study on the binding properties of a lectin isolatedfrom Codium fragile subspecies tomentosoides (CFT) indicatesthat this lectin recognizes the GalNAc1 sequence at both reducingand nonreducing ends. In this study, the carbohydrate specificityof CFT was further characterized by quantitative precipitin(QPA) and inhibition of lectin-enzyme binding assays. Of theglycoforms tested for QPA, all asialo-GalNAc1 containing glyco-proteinsreacted well with the lectin. Asialo hamster and ovine submandibularglycoproteins, which contain almost exclusively Tn (GalNAclSer/Thr)residues as carbohydrate side chains, and Streptococcus typeC polysaccharide completely precipitated the lectin added, whilethe GalNAcβcontaining Tamm-Horsfall Sd(a+) glycopro-teinand its asialo product were inactive. Among the oligo-saccharidestested for inhibiting lectin-glycoprotein interaction, GalNAc13GalNAcβ13Gal14Galβ14GIc(Fp)and Galβ13GalNAc1benzyl (T) were the best, and about 125-foldmore active than GalNAc They were about 3.3, 6.6, and 43 timesmore active than Tn containing glycopeptides, GalNAc13(LFuc12)Gal(Ah) and Galβ13GalNAc(T), respectively. From the presentand previous results, it is concluded that the combining siteof CFT is probably of a groove type that recognizes from GalNAclto pentasaccharide(Fp). The carbohydrate specificity of thislectin can be constructed and summarized in decreasing orderby lectin determinants as follows: Fp and T > Tn cluster> Ah >>I/II. carbohydrate specificities Codium fragile tomentosoides glycoprotein binding lectins  相似文献   

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