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1.
A factor having the expected properties of the in vivo oxidant responsible for inactivating the in vivo light-activated chloroplast coupling factor 1 (CF 1) has been partially purified from cell-free extracts of Dunaliella salina. This factor is highly polar, weakly acidic, and relatively temperature stable. The ability of this factor to inactivate light-activated CF 1 is prevented if it is pretreated with reductants such as dithiothreitol. The factor has virtually no effect on the ethanol-induced, Mg 2+ -dependent ATPase activity of the isolated CF 1. 相似文献
2.
The sensitivity of the catalytic activities of the D. salina chloroplast coupling factor 1 (CF1) to chemical modification by N-ethylmaleimide has been investigated. When D. salina thylakoid membranes are treated with N-ethylmaleimide, both photophosphorylation and the inducible CF1 ATPase activity are partially (approx. 60%) inhibited. The inhibition of both activities does not require the presence of a proton-motive force, and the inhibition of photophosphorylation is directly related to the N-ethylmaleimide-covalent modification of CF1 as shown by the time-course for the inhibition and the maximal extent of inhibition. Treatment of the purified, latent, D. salina CF1 with low concentrations of N-ethylmaleimide also results in the partial (approx. 60%) inhibition of the inducible ATPase activity (I50 approximately 50 microM). The inhibition does not require the presence of the chemical modifier during the activation of the enzyme. N-ethylmaleimide-induced inhibition of the ATPase activity of either membrane-bound or solubilized CF1 is partially reversed by either prolonged incubation at low concentrations of N-ethylmaleimide or short incubation times at high concentrations of N-ethylmaleimide. The results are interpreted as indicating multiple binding sites on the D. salina CF1 that have different rates of reactivity with N-ethylmaleimide. Those sites (or site) that react rapidly with N-ethylmaleimide cause(s) an inhibition of both ATP synthase and ATPase activities, whereas those sites (or site) that react more slowly partially restore(s) the original ATPase activity. The effects of N-ethylmaleimide on the catalytic activity of D. salina CF1 are probably mediated by N-ethylmaleimide-induced conformational changes of the enzyme. 相似文献
3.
Preillumination of intact cells of the eukaryotic, halotolerant, cell-wall-less green alga Dunaliella salina induces a dark ATPase activity the magnitude of which is about 3–5-fold higher than the ATPase activity observed in dark-adapted cells. The light-induced activity arises from the activation and stabilization in vivo of chloroplast coupling factor 1 (CF 1). This activity, 150–300 μmol ATP hydrolyzed/mg Chl per h, rapidly decays (with a half-time of about 6 min at room temperature) in intact cells but only slowly decays (with a half-time of about 45 min at room temperature) if the cells are lysed by osmotic shock immediately after illumination. The activated form of the ATPase in lysed cells is inhibited if the membranes are treated with ferri- but not ferrocyanide, suggesting that the stabilization of the activated form of CF 1 is due to the reduction of the enzyme in vivo in the light. 相似文献
4.
We investigated the binding of subunit δ to solubilized chloroplast ATPase. Purified δ was covalently labeled with eosin 5-isothiocyanate and its rotational correlation time was determined by a photoselection technique as a function of added CF 1 (containing δ) and of CF 1(−δ) (lacking δ). In aqueous buffer the rotational correlation time of labeled δ was 33 ns. This is compatible with a rather elongated shape with the dimensions 2 b = 100 Å/2 a = 28 Å. Binding of δ to CF 1 decreased the rotational correlation time about 10-fold. The result was a biphasic decay of the laser flash-induced absorption anisotropy which was analyzed to yield the proportion of δ (bound to CF 1) relative to δ (free). CF 1(−δ), which completely lacked the δ-subunit, bound one δ (mol/mol) with high affinity ( Kd ≈ 100 nM) and at least another δ with about 20-fold lower affinity. The δ-containing CF 1, revealed only the low-affinity site(s) for δ. This was compatible with a 1:1 stoichiometry of δ in isolated CF 1. 相似文献
5.
The Pt 2 (II) isomeric terminal hydrides [(CO)(H)Pt(μ-PBu t 2) 2Pt(PBu t 2H)]CF 3SO 3 (1a), and [(CO)Pt(μ-PBu t 2) 2Pt(PBu t 2H)(H)]CF 3SO 3 (1b), react rapidly with 1 atm of carbon monoxide to give the same mixture of two isomers of the Pt 2 (I) dicarbonyl [Pt 2(μ-PBu t 2)(CO) 2(PBu t 2H) 2]CF 3SO 3 (3-Pt); the solid state structure of the isomer bearing the carbonyl ligands pseudo- trans to the bridging phosphide was solved by X-ray diffraction. A remarkable difference was instead found between the reactivity of 1a and 1b towards carbon disulfide or isoprene. In both cases 1b reacts slowly to afford [Pt 2(μ-PBu t 2)(μ,η 2,η 2-CS 2)(PBu t 2H) 2]CF 3SO 3 (4-Pt), and [Pt 2(μ-PBu t 2)(μ,η 2,η 2-isoprene) (PBu t 2H) 2]CF 3SO 3 (6-Pt), respectively. In the same experimental conditions, 1a is totally inert. A common mechanism, proceeding through the preassociation of the incoming ligand followed by the P---H bond formation between one of the bridging P atoms and the hydride ligand, has been suggested for these reactions. 相似文献
6.
The X-ray structure is reported for the complex Cu 2(medpco-2H)Cl 2, (medpco = N, N′-bis- N, N-dimethylaminoethyl)pyridine-2,6-dicarboxamide 1-oxide. The complex is triclinic,
, a=8.313(4), B=11.403(5), C=11.611(3) Å, =91.66(3), β=108.99(4), γ=109.60(3)° and Z=2. The deprotonated ligand (medpco-2H) 2− acts as a binulceating ligand, producing an N-oxide-bridged complex. Each copper in Cu 2(medpco-2H)Cl 2 is five-coordinate, being coordinated by a bridging N-oxide oxygen, a deprotonated amide nitrogen, a tertiary amine nitrogen and two bridging chlorides. The complex does not exhibit significant magnetic interaction, and this may be the result of distortion of the bridging geometry from planarity. A range of other, apparently N-oxide-bridged, complexes of the type Cu 2(medpco-2H)X 2 is reported. The complex Cu 2(medpco-2H)Br 2·H 2O is strongly antiferromagnetic, with magnetic data closely fitting the expected binuclear structure. 相似文献
7.
Small-angle neutron scattering experiments were performed in dilute aqueous solutions of chloroplast F 1-ATPase. By contrast variation in 1H 2O/ 2H 2O mixtures and when using different concentrations of glycerol in 2H 2O, structural information on the spatial distribution of dry protein and water was obtained. The maximum distance within latent and active CF 1 was 12 nm. the shape of CF 1 was globular. The total volume of CF 1 was 900 nm 3, and its dry volume (excluding the volume of one water molecule per two exchangeable hydrogen atoms) was 400 nm 3. A volume of 670 nm 3 was inaccessible to glycerol at low glycerol concentrations (less than 25%). At higher concentrations (up to 50%) a volume of 460 nm 3 was excluded to glycerol. Within the resolution of our experiment (1.6 nm) there was no evidence for particular water-rich regions or of secluded water spaces or any particular places for glycerol exchange. Upon thiol activation of the latent enzyme only small changes in structure were detectable just at the limits of the experimental error. They suggest an enhancement of the surface roughness. 相似文献
8.
为了探讨环境激素类物质邻苯二甲酸二乙酯(DEP)和壬基酚(NP)对海洋微藻的联合毒性效应,选取杜氏盐藻( Dunaliella salina)为受试生物,以环境激素对杜氏盐藻单一暴露的96h EC 50的毒性效应作为一个毒性单位(IU),采用毒性单位法比较研究了DEP和NP单一暴露以及两者以三种不同混合比例(毒性单位比:1:1、1:4和4:1)暴露对杜氏盐藻的细胞生长、叶绿体色素含量、可溶性蛋白含量、SOD活性以及最大光能转化效率(Fv/Fm)的影响.实验结果表明:DEP和NP单一暴露对杜氏盐藻的96h EC 50分别为69.54 mg/L和1.47 mg/L,两种环境激素对杜氏盐藻均有抑制作用,且NP较DEP对杜氏盐藻的毒性更强.DEP和NP联合暴露较单一暴露对杜氏盐藻的细胞生长、叶绿体色素和可溶性蛋白的合成有较强的抑制作用,两种环境激素在毒性单位比为1:1、1:4、4:1三个比例水平上的联合毒性效应均表现为协同效应,其中比例为1:1的协同效应最强. 相似文献
9.
We have measured the inhibitory potencies of several local anesthetics (procaine, lidocaine, tetracaine and dibucaine) and related compounds (chlorpromazine, procainamide and propranolol) on the ATPase activities of bovine heart submitochondrial particles and purified F 1 extracted from these particles. All of these agents cause inhibition of ATPase in F 1 as well as in submitochondrial particles. A linear relationship is found between the log of the octanol/water partition coefficients and the log of the concentrations required for 50% inhibition of F 1. Sedimentation velocity ultracentrifugation and polyacrylamide gel electrophoresis showed that 1.0 mM tetracaine caused partial dissociation of the F 1 complex. Complete reversibility of the enzyme inhibitory effects was demonstrated, however. This work shows that local anesthetics can affect protein structure and enzyme activity without the mediation of lipid. 相似文献
10.
The effects of N-ethylmaleimide (NEM) on mouse platelet serotonin (5-HT) and 86Rb + uptake were studied. The 5-HT transport system showed a biphasic response to increasing concentrations of NEM, with low concentrations (25–50 μM) stimulating and high concentrations (200–400 μM) inhibiting 5-HT transport. Fluoxetine, an inhibitor of the platelet 5-HT transporter, blocked NEM-induced stimulation of 5-HT transport. The kinetics of 5-HT uptake indicated that NEM (50 μM) markedly increased the maximal rate of 5-HT transport ( Vmax control = 28.4±1.4 pmol/10 8 platelets/4 min vs Vmax NEM = 64.5±9.5 pmol/10 8 platelets/4 min but had no significant effect on the Km value. Platelet Na + K + ATPase activity was determined by measuring 86Rb + uptake. Platelet 86Rb + uptake showed a biphasic response to NEM, with low concentrations (25–100 μM) significantly stimulating and high concentrations (400 μM) inhibiting uptake. These changes in platelet 86Rb + uptake paralleled the biphasic changes in 5-HT transport. In the presence of fluoxetine, 5-HT transport was markedly inhibited but no change in the ability of NEM to stimulate 86Rb + uptake was observed. These data suggest that low concentrations of NEM activate plasma membrane Na + K + ATPase which results in a marked stimulation of platelet 5-HT transport. 相似文献
11.
1. 1. Fuscin, a mould metabolite, is a colored quinonoid compound which reacts readily with −SH groups to give colorless addition derivatives. 2. 2. Binding of fuscin to mitochondria has been monitored spectrophotometrically. Fuscin binding is prevented by −SH reagents such as N-ehylmaleimide, N-Methylmaleimide, mersalyl or p-chloromercuribenzoate. Conversely, fuscin prevents the binding of −SH reagents as shown with N-[14C]ethylmaleimide. Once bound to mitochondria, fuscin is not removable by washing of mitochondria. 3. 3. High affinity-fuscin binding sites (Kd = 1 μM, N = 4–8 nmoles/mg protein) are present in whole mitochondria obtained from rat heart, rat liver, pigeon heart or yeast (Candida utilis). They are lost upon sonication but are still present in digitonin inner membrane + matrix vesicles. On the other hand, lysis of mitochondria by Triton X-100 does not increase the number of high affinity binding sites indicating that all these sites are accessible to fuscin in whole mitochondria. The number of fuscin high affinity sites appears to correlate with the glutathione content of mitochondrial preparations. 4. 4. Fuscin as well as N-ethylmaleimide and avenaciolide are penetrant SH-reagents; 5. 5. Fuscin interferes with the ADP-stimulated respiration of mitochondria on NAD-linked substrates, several functions of the mitochondrial respiratory apparatus being inhibited by fuscin in a non-competitive manner, but to various extents: (a) The electron transfer chain (Ki in the range of 0.1 mM); (b) the lipoamide dehydrogenase system (Ki = 5–10 μM); (c) the transport systems of phosphate (Ki ≈ 20 μM) and of glutamate (Ki = 3–5 μM); (d) the ADP transport, indirectly (Ki ≈ 10 μM). 6. 6. Like N-ethylmaleimide, fuscin inhibits the glutamate-OH− carrier, the inhibition of that carrier bringing about an apparent increase of aspartate entry in glutamate-loaded mitochondria by the glutamate-aspartate carrier. 7. 7. The inhibition of phosphate transport by fuscin probably accounts for the inhibition of the reduction of endogenous NAD by succinate in intact pigeon heart mitochondria. 8. 8. By binding the −SH groups of mitochondrial membrane specifically unmasked by addition of micromolar amounts of ADP, fuscin, like N-ethylmaleimide, prevents the functioning of ADP translocation. 9. 9. Because of their specific and analogous effects on some well defined mitochondrial functions such as glutamate transport and ADP transport, fuscin and N-ethylmaleimide can be distinguished from other −SH reagents. The lipophilic nature of fuscin and N-ethylmaleimide which accounts for the accessbility of these compounds to hydrophobic sites in the mitochondrial membrane or on the matrix side of this membrane may be partly responsible for their characteristic inhibitory effects on mitochondrial functions.
Abbreviations: DTNB, 5,5′-dithio-bis-(2-nitrobenzoic acid); PCMB, p-chloromercuribenzoate 相似文献
12.
The phosphinoalkenes Ph 2P(CH 2) nCH=CH 2 ( n= 1, 2, 3) and phosphinoalkynes Ph 2P(CH 2) n C≡CR (R = H, N = 2, 3; R = CH 3, N = 1) have been prepared and reacted with the dirhodium complex (η−C 5H 5) 2Rh 2(μ−CO) (μ−η 2−CF 3C 2CF 3). Six new complexes of the type (ν−C 5H 5) 2(Rh 2(CO) (μ−η 1:η 1−CF 3C 2CF 3)L, where L is a P-coordinated phosphinoalkene, or phosphinoalkyne have been isolated and fully characterized; the carbonyl and phosphine ligands are predominantly trans on the Rh---Rh bond, but there is spectroscopic evidence that a small amount of the cis-isomer is formed also. Treatment of the dirhodium-phosphinoalkene complexes with (η−CH 3C 5H 4)Mn(CO) 2thf resulted in coordination of the manganese to the alkene function. The Rh 2---Mn complex [(η−C 5H 5) 2Rh 2(CO) (μ−η 1:η 1−CF 3C 2CF 3) {Ph 2P(CH 2) 3CH=CH 2} (η−CH 3C 5H 4)Mn(CO) 2] was fully characterized. Simi treatment of the dirhodium-phosphinoalkyne complexes with Co 2(CO) 8 resulted in the coordination of Co 2(CO) 6 to the alkyne function. The Rh 2---Co 2 complex [(η−C 5H 5) 2Rh 2(CO) (μ−η 1:η 1−CF 3C 2CF 3) {Ph 2PCH 2C≡CCH 3}Co 2(CO) 2], C 37H 25Co 2F 6O 7PRh 2, was fully characteriz spectroscopically, and the molecular structure of this complex was determined by a single crystal X-ray diffraction study. It is triclinic, space group
( Ci1, No. 2) with a = 18.454(6), B = 11.418(3), C = 10.124(3) Å, = 112.16(2), β = 102.34(3), γ = 91.62(3)°, Z = 2. Conventional R on | F| was 0.052 fo observed ( I > 3σ( I)) reflections. The Rh 2 and Co 2 parts of the molecule are distinct, the carbonyl and phosphine are mutually trans on the Rh---Rh bond, and the orientations of the alkynes are parallel for Rh 2 and perpendicular for Co 2. Attempts to induce Rh 2Co 2 cluster formation were unsuccessful. 相似文献
13.
Guanosine triphosphate and formycin triphosphate (FTP) in the presence of excess Mg 2+ can bind to empty non-catalytic sites of spinach chloroplast ATPase (CF 1). This results in a greatly reduced capacity for ATP hydrolysis compared to the enzyme with non-catalytic sites filled with ATP. With two GTP bound at non-catalytic sites the inhibition is about 90%; with two FTP bound about 80% inhibition is obtained. Binding and release of the nucleotides from the non-catalytic sites are relatively slow processes. Exposure of CF 1 with one or two empty non-catalytic sites to 5–10 μM FTP or GTP for 15 min suffices for about 50% of the maximum inhibition. Reactivation of CF 1 after exposure to higher FTP or GTP concentrations requires long exposure to 2 μM EDTA. The findings show that, contrary to previous assumptions, GTP can bind tightly to non-catalytic sites of CF 1. They suggest that the presence of adenine nucleotides at non-catalytic sites might be essential for high catalytic capacity of the F 1 ATPases. 相似文献
14.
New mixed metal complexes SrCu 2(O 2CR) 3(bdmap) 3 (R = CF 3 (1a), CH 3 (1b)) and a new dinuclear bismuth complex Bi 2(O 2CCH 3) 4(bdmap) 2(H 2O) (2) have been synthesized. Their crystal structures have been determined by single-crystal X-ray diffraction analyses. Thermal decomposition behaviors of these complexes have been examined by TGA and X-ray powder diffraction analyses. While compound 1a decomposes to SrF 2 and CuO at about 380°C, compound 1b decomposes to the corresponding oxides above 800°C. Compound 2 decomposes cleanly to Bi 2O 3 at 330°C. The magnetism of 1a was examined by the measurement of susceptibility from 5–300 K. Theoretical fitting for the susceptibility data revealed that 1a is an antiferromagnetically coupled system with g = 2.012(7), −2 J = 34.0(8) cm −1. Crystal data for 1a: C 27H 51N 6O 9F 9Cu 2Sr/THF, monoclinic space group P2 1/ m, A = 10.708(6), B = 15.20(1), C = 15.404(7) Å, β = 107.94(4)°, V = 2386(2) Å 3, Z = 2; for 1b: C 27H 60N 6O 9Cu 2Sr/THF, orthorhombic space group Pbcn, A = 19.164(9), B = 26.829(8), C = 17.240(9) Å, V = 8864(5) Å 3, Z = 8; for 2: C 22H 48O 11N 4Bi 2, monoclinic space group P2 1/ c, A = 17.614(9), B = 10.741(3), C = 18.910(7) Å, β = 109.99(3)°, V = 3362(2) Å 3, Z = 4. 相似文献
15.
The chloro complexes trans-[Pt(Me)(Cl)(PPh 3) 2], after treatment with AgBF 4, react with 1-alkynes HC---C---R in the presence of NEt 3 to afford the corresponding acetylide derivatives trans-[Pt(Me) (C---C---R) (PPh 3) 2] (R = p-tolyl (1), Ph (2), C(CH 3) 3 (3)). These complexes, with the exception of the t-butylacetylide complex, react with the chloroalcohols HO(CH 2) nCl ( n = 2, 3) in the presence of 1 equiv. of HBF 4 to afford the alkyl(chloroalkoxy)carbene complexes trans-[Pt(Me) {C[O(CH 2) nCl](CH 2R) } (PPh 3) 2][BF 4] (R = p-tolyl, N = 2 (4), N = 3 (5); R=Ph, N = 2 (6)). A similar reaction of the bis(acetylide) complex trans-[Pt(C---C---Ph) 2(PMe 2Ph) 2] with 2 equiv. HBF 4 and 3-chloro-1-propanol affords trans-[Pt(C---CPh) {C(OCH 2CH 2CH 2Cl)(CH 2Ph) } (PMe 2Ph) 2][BF 4] (7). T alkyl(chloroalkoxy)-carbene complex trans-[Pt(Me) {C(OCH 2CH 2Cl)(CH 2Ph) } (PPh 3) 2][BF 4] (8) is formed by reaction of trans-[Pt(Me)(Cl)(PPh 3) 2], after treatment with AgBF 4 in HOCH 2CH 2Cl, with phenylacetylene in the presence of 1 equiv. of n-BuLi. The reaction of the dimer [Pt(Cl)(μ-Cl)(PMe 2Ph)] 2 with p-tolylacetylene and 3-chloro-1-propanol yields cis-[PtCl 2{C(OCH 2CH 2CH 2Cl)(CH 2C 6H 4- p-Me}(PMe 2Ph)] (9). The X-ray molecular structure of (8) has been determined. It crystallizes in the orthorhombic system, space group Pna2 1, with a = 11.785(2), B = 29.418(4), C = 15.409(3) Å, V = 4889(1) Å 3 and Z = 4. The carbene ligand is perpendicular to the Pt(II) coordination plane; the PtC(carbene) bond distance is 2.01(1) Å and the short C(carbene)-O bond distance of 1.30(1) Å suggests extensive electronic delocalization within the Pt---C(carbene)---O moietry. 相似文献
16.
The effects of histamine (HA), and selective HA, H 1-, H 2 and H 3-receptor agonists on cyclic AMP formation were investigated in intact thick and duck pineal glands. HA potently stimulated the pineal cyclic AMP formation. The effect of HA was mimicked fully by N- methylated histamines, and partially by several histaminergic drugs: 2-thiazolylethylamine (H 1), amthamine (H 2) and R- methylhistamine (H 3). Dimaprit, another selective H 2-agonist showed marginal activity. Forskolin highly potentiated the action of HA, and only weakly affected the effects of 2-thiazolyethylamine and amthamine. In the chick pineal, the stimulatory effects of HA and the tested histaminergic drugs were not blocked by mepyramine and thioperamide (H 1- and H 3-blockers, respectively), but they were antagonized by H 2-receptor selective compounds ranitidine and aminopotentidine, which, however, acted in a noncompetitive manner. Another H 2-selective blocker zolantidine antagonized the HA effect only when used at very high (30–100 μM) concentrations. In the duck pineal, the stimulatory effect of HA on cyclic AMP production was unaffected by mepyramine (H 1), thioperamide (H 3), and ranitidine (H 2), and only partially inhibited by the H 2-blocker aminopotentidine. Electrophysiological experiments revealed that HA is capable of evoking inward currents in most of the tested cells acutely isolated from chick pineal gland. The present findings further indicate that the pharmacological profile of the avian pineal HA receptor, whose stimulation leads to activation of cyclic AMP production, is different from any known HA receptor type (H 1, H 2, H 3), and suggest the existence of either an avian-specific HA receptor, or a novel HA receptor subtype. Electrophysiological data suggest that the pineal HA receptor may be somehow linked to activation of an ionic channel. 相似文献
17.
UV irradiation of the ATPase (CF 1) from spinach chloroplasts in the presence of 3'-arylazido-β-alanyl-8-azido ATP (8,3'-DiN 3ATP) results in a nucleotide-dependent inactivation of the enzyme and in a nucleotide-dependent formation of -β cross-links. The results demonstrate an interfacial localization of the nucleotide binding sites on CF 1. 相似文献
18.
[MnL](ClO 4) 2 (L = N, N′, N″-tris(2-hydroxypropyl)-1,4,7-triazacyclononane) has been tested for catalyzing sulfide oxidation. In the presence of this complex, ethyl phenyl sulfide, butyl sulfide and phenyl sulfide are completely oxidized to the corresponding sulfoxides and sulfones with H 2O 2 as the oxidant. 2-Chloroethyl phenyl sulfide oxidation yield 2-chloroethyl phenyl sulfone and phenyl vinyl sulfone. In ethyl phenyl sulfide oxidation, effects of complex and H 2O 2 concentration and temperature on the reaction rate have been discussed. Through controlling reaction conditions, ethyl phenyl sulfoxide and ethyl phenyl sulfone may be produced selectively. The UV–Vis and electron paramagnetic resonance (EPR) studies on catalyst solution indicate that metal centre of the complex is transformed from Mn(II) to Mn(IV) after the addition of H 2O 2. At 25 °C, rate constant for ethyl phenyl sulfide oxidation is 4.38 × 10 −3 min −1. 相似文献
19.
Chitosans, prepared by homogeneous N-deacetylation of chitin, with degrees of N-acetylation ranging from 4 to 60% ( FA = 0·04 to 0·60) exhibiting full water solubility and known random distribution of acetyl groups, were degraded with lysozyme. Initial degradation rates ( r) were determined from plots of the viscosity decrease (Δ1/[η]) against time of degradation. The time course of degradation of chitosans with lysozyme were non-linear, while the time course of degradation of chitosans with an oxidative-reductive depolymerization reaction (using H 2O 2) showed the expected linear relationship for a first-order, random depolymerization reaction, independent of the chemical composition of the chitosan. The effect of lysozyme concentration and substrate concentration on the initial degradation rates were determined, showing that this lysozyme-chitosan system obeys Michaelis-Menten kinetics. The initial degradation rates of chitosan with lysozyme increased strongly with increasing fraction of acetylated units (FA). From a Michaelis-Menten analysis of the degradation data that assumes different catalytic activities of lysozyme for the different hexameric substrates in the polysaccharide chain, it is concluded that the hexameric substrates that contain three-four or more acetylated units contribute mostly to the initial degradation rate when lysozyme degrades partially N-acetylated chitosans. A chitosan with a very low fraction of acetylated units (FA = 0·010) was studied as an enzyme inhibitor. Initial degradation rates of chitosan (with different FA values) decreased as the inhibitor concentration increased, while the relative rates stayed constant, indicating that the ratio between initial reaction rates for productive sites (hexamers containing three-four or more N-acetylated units) are unaffected by non-productive sites, as deduced from the theory of competing substrates. 相似文献
20.
The new tripodal phosphine CH 3C{CH 2P( m-CF 3C 6H 4) 2} 3, CF 3PPP, was prepared by reacting CH 3C(CH 2Br) 3 with Li +P( m-CF 3C 6H 4) 2−, the latter being best obtained by adding Li +N iPr 2− to PH( m-CF 3C 6H 4) 2. The rhodium complexes [RhCl(CO)(CF 3PPP)], [Rh(LL)(CF 3PPP)](CF 3SO 3) (LL = 2 CO or NBD), [RhX 3(CF 3PPP)], [RhX(MeCN) 3(CF 3PPP)](CF 3SO 3) 2 (X = H and Cl), [RhCl 2(MeCN)(CF 3PPP)](CF 3SO 3) and [Rh(MeCN) 3(CF 3PPP)](CF 3SO 3) 3 were prepared and characterized. The X-ray crystal structure of [Rh(NBD)(CF 3PPP)](CF 3SO 3) is reported. The lower oxygen sensitivity of the CF 3PPP rhodium(I) complexes, relative to the corresponding species with the parent ligand CH 3C(CH 2PPh 2) 3, is attributed to the higher effective nuclear charge on the metal centers caused by the presence of the six CF 3 substituents on the terdentate phosphine. A similar effect may be responsible for the easier hydrolysis of the CF 3PPP-containing, cationic rhodium(III) complexes relative to the corresponding compounds of the parent ligand. 相似文献
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