Addition of ATP to chloroplasts causes a reversible 25-30% decrease in chlorophyll fluorescence. This quenching is light-dependent, uncoupler insensitive but inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethyl urea (DCMU...
详细信息
Addition of ATP to chloroplasts causes a reversible 25-30% decrease in chlorophyll fluorescence. This quenching is light-dependent, uncoupler insensitive but inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethyl urea (DCMU) and electron acceptors and has a half-time of 3 min. Electron donors to PS (photosystem) I cannot overcome the inhibitory effect of DCMU;apparently light activation depends on the reduced state of plastoquinone. fluorescence emission spectra recorded at -***. C indicate that ATP treatment increases the amount of excitation energy transferred to PS I. fluorescence induction curves indicate that ATP treatment decreases both the initial (f0) and variable (fv) fluorescence such that the ratio offv to the maximum (fm) yield is unchanged. The initial sigmoidal phase of induction is slowed down by ATP treatment and is quenched 3-fold more than the exponential slow phase, the rate of which is unchanged. A plot offv against area above the induction curve was identical plus or minus ATP. ATP treatment can alter quantal distribution between PS II and PS I without altering PS II-PS II interaction. The effect of ATP strongly resembles in its properties the phosphorylation of the light-harvesting complex by a light activated, ATP-dependent protein kinase found in chloroplast membranes and may be the basis of physiological mechanisms which contribute to slow fluorescence quenching in vivo and regulate excitation energy distribution between PS I and PS II. The sensor for this regulation may be the redox state of plastoquinone.
Detailed histochemical studies have been performed on the distribution of the nuclei innervating the supraoptic nucleus (SO) in the whole brain after horseradish peroxidase (HRP) injections through fine glass micropip...
详细信息
Detailed histochemical studies have been performed on the distribution of the nuclei innervating the supraoptic nucleus (SO) in the whole brain after horseradish peroxidase (HRP) injections through fine glass micropipettes (2 to 8 micrograms ) into the SO of 39 Wistar strain rats. The chromatogenic reaction was carried out according to the Mesulam's (1976) No. 8 procedure. Successful HRP injections resulted in labeling in various regions of the brain. The following conclusions were drawn from the analysis of these successful cases. All the nuclei of the subthalamus and posthypothalamus innervate the SO whereas only a few neurons of the hypothalamic arcuate and ventromedial nuclei probably send axons to it. The afferent monoaminergic fibers arise largely from the B7 and B8, and to a certain extent from the A6 and A10 cell groups. The septum, diagonal band nucleus and amygdala project directly to the SO while the olfactory tubercle and pyriform cortex may not. The mesencephalic central gray has a high possibility to project directly to it. The possibility that the hippocampus sends axons to the SO remains to be fully proven. A few small multipolar cells clearly revealed by the test in the SO should be non-secretory intercalated neurons.
Substrate specificity of .alpha.-L-arabinofuranosidase from plant S. japonica was examined using 3 kinds of arabinodisaccharides prepared from natural sources or synthetically. This enzyme hydrolyzed arabinofuranosyla...
详细信息
Substrate specificity of .alpha.-L-arabinofuranosidase from plant S. japonica was examined using 3 kinds of arabinodisaccharides prepared from natural sources or synthetically. This enzyme hydrolyzed arabinofuranosylarabinoses which had either on .alpha.-(1 .fwdarw. 3) or a .alpha.-(1 .fwdarw. 5) linkage but hydrolyzed arabinopyranosyl-arabinose having a .alpha.-(1 .fwdarw. 5) linkage to a lesser degree. .alpha.-L-Arabinofuranosidase (.alpha.-L-arabinofuranoside arabinofuranohydrolase, EC 3.2.1.55), which is an exo-enzyme, degraded beet araban incompletely. Arabinose oligomers and galactose-containing fragments, isolated following acid hydrolysis of araban, were incompletely degraded by the enzyme. The reasons for the incomplete degradation were explained by the novel finding of (1 .fwdarw. 2) linkages and arabinopyranosides and the inclusion of trace amounts of galactose into the carbohydrate chain of araban. This enzyme was practically non-reacting with the hydroxyprolyl-arabinose linkage of glycopeptides from plant cell walls.
Steady-state velocity studies using a substrate regenerating system showed that efrapeptin, citreoviridin and aurovertin inhibit both membrane-bound and soluble mitochondrial ATPase (coupling factor f1) from Trypanoso...
详细信息
Steady-state velocity studies using a substrate regenerating system showed that efrapeptin, citreoviridin and aurovertin inhibit both membrane-bound and soluble mitochondrial ATPase (coupling factor f1) from Trypanosoma cruzi. Maximal inhibitions of ATP hydrolysis produced by efrapeptin and citreoviridin were 100-93%, while the maximal inhibition produced by aurovertin was 40%. Half-maximal inhibitory concentrations decreased in the order citreoviridin greater than aurovertin greater than efrapeptin. Dissociation constants (KD) for the inhibitor-f1 complex were 81 nM (efrapeptin), 6.6 muM (aurovertin) and 40 muM (citreoviridin); KD values for the membrane-bound f1 were 2-4 fold higher than for soluble f1. Representation of efrapeptin inhibition data in the Hill form yielded straight lines (n = 1) while the same representation of citreoviridin inhibition yielded concave down plots. In contrast to the immediate effect of citreoviridin and aurovertin, efrapeptin inhibition was time-dependent. The onset of inhibition, which was pseudo-first-order with respect to efrapeptin, indicated that ATP may promote the binding of efrapeptin to the enzyme. The kinetics of ATP hydrolysis by T. cruzi ATPase as a function MgATP concentration could be explained by the presence of two substrate sites on the enzyme, interacting in such a way that the binding and catalytic events at one site were conformationally linked to the events at the other site, as with the mammalian ATPase. When the antibiotics were assayed at increasing substrate concentrations, efrapeptin produced a linear, mixed-type inhibition whereas citreoviridin produced a parabolic noncompetitive-type inhibition. The aurovertin effect was unusual since the extent of inhibition was greater at high substrate concentrations. Maximal concentrations of all the assayed antibiotics linearized the biphasic double reciprocal plot of control ATPase activity. Comparison of T. cruzi and mammalian f1 responses to the assayed antibiotic
Structurally and functionally different tobacco [Nicotiana tabacum] chloroplasts were subjected to digitonin treatment and subsequent fractional centrifugation. The light-harvesting chlorophyll a/chlorophyll b-protein...
详细信息
Structurally and functionally different tobacco [Nicotiana tabacum] chloroplasts were subjected to digitonin treatment and subsequent fractional centrifugation. The light-harvesting chlorophyll a/chlorophyll b-protein complex was enriched in the most dense fraction regardless of the presence of grana in the original preparation. Evidently, isolated thylakoid membranes and fragments which contain sufficient light-harvesting protein may, under appropriate ionic conditions, form aggregates even when they originate from unstacked thylakoid systems. Comparative studies offluorescence properties and polypeptide composition of the thylakoids suggest that the light-harvesting protein does not contribute significantly to the fluorescence spectrum of isolated chloroplasts as long as this protein is intimately associated with the photosystem II (PS II) pigment-protein complex responsible for the 685 nm emission. While the PS II-deficient mutant chloroplasts of the variegated tobacco cv. NC 95 lacked both the 685 nm fluorescence component and 2 or 3 PS II proteins, 1 of these proteins was very prominent in these chlorophyll b-deficient mutant thylakoids which also displayed an intense 685 nm fluorescence peak. This correlation supports the contention that a 45 kdalton polypeptide is an apoprotein of pigments associated with the PS II reaction center.
The inhibitor and substrate specificities of deoxythymidine (dThd) kinase purified from herpes simplex virus (HSV Type 1) were studied. A number of nucleosides and nucleoside analogs were phosphorylated by the virus c...
详细信息
The inhibitor and substrate specificities of deoxythymidine (dThd) kinase purified from herpes simplex virus (HSV Type 1) were studied. A number of nucleosides and nucleoside analogs were phosphorylated by the virus coded enzyme. These included several compounds structurally related to 9-(2-hydroxyethoxymethyl)guanine (acyclovir), a potent inhibitor of HSV replication. Some contained guanine with 9-substituents differing from those of acyclovir by methylene additions, methylene and thioether substitutions for the ether oxygen, and branching on the distal side of the ether oxygen. Others were various 2-substituted 6-hydroxypurines with the 9-(2-hydroxyethoxymethyl) substituent. A limitation of the specificity of the enzyme with guanine derivatives was the lack of phosphorylation of any derivative with an acyclic moiety branched on the proximal side of the ether oxygen. Many of the compounds that were phosphorylated were subsequently found to inhibit HSV replication. Such compounds apparently inhibited HSV replication via the same route of activation previously described for acyclovir. Moreover, several compounds not phosphorylated by the enzyme did not inhibit replication. Some other acyclic nucleoside analogs that were phosphorylated were not good antivirals, indicating that phosphorylation catalyzed by the HSV dThd kinase was not sufficient for inhibition of viral replication to occur. These results evidently emphasize the importance of the specificity of cellular kinases and the HSV DNA polymerase to the mechanism of antiviral activity. The dThd kinase from Vero cells was also purified. With this host cell enzyme, kinetic constants of known antiviral compounds were determined and compared to those of dThd (relative V''max;K''m: dThd (100;1.3 .mu.M), 5-iodo-2''-deoxyuridine (87;1.8 mM), 5-trifluoromethyl-2''-deoxyuridine (91;1.2 .mu.M), 5-bromo-2''-deoxycytidine (5;580 .mu.M) and 9-.beta.-D-arabinofuransyolthymine (23;2300 .mu.M). None of the purine acyclic nucleos
Human serum and fetal calf serum are compared in terms of their ability to modify the biochemical and immunological properties of the schistosomular surface. Artificially transformed schistosomula were incubated in th...
详细信息
Human serum and fetal calf serum are compared in terms of their ability to modify the biochemical and immunological properties of the schistosomular surface. Artificially transformed schistosomula were incubated in the presence of serum for 24 h and then radioiodinated using the chloramine T method. With this method only lipids are labeled. fetal calf serum produces a net loss of lipids from the schistosomula, particularly of mono- and diglycerides. Human serum promotes not only a loss of mono- and diglycerides, but also a substantial uptake of cholesterol and triglycerides. Schistosomula recovered from the lungs of mice could also be labeled and contained, besides triglycerides, an increased amount of cholesterol esters. The modulation of surface lipids in worms cultured with human serum correlates with the observation that such schistosomula develop significantly greater protection against eosinophil-mediated cytotoxicity in vitro than do individuals incubated with fetal calf serum. Schistosomula cultured in the presence of either human serum or fetal calf serum develop the same degree of protection against complement-dependent lethal antibody;this result indicates that resistance against complement-mediated damage may be independent of the uptake of cholesterol and/or triglycerides, and might involve only limited alterations in the surface configuration of the schistosomulum.
Particulate material from cucumber hypocotyls was purified by differential centrifugation and agarose gel chromatography. The fraction was heterogeneous in nature and contained both phytochrome and ATPase activity. Th...
详细信息
Particulate material from cucumber hypocotyls was purified by differential centrifugation and agarose gel chromatography. The fraction was heterogeneous in nature and contained both phytochrome and ATPase activity. The latter consisted of at least 2 different components, a non-specific acid phosphatase and a potassium stimulated ATPase (K+-ATPase). The K+-ATPase appeared to be strongly inhibited by Ca+2 and was subject to photoregulation by red and far red light (R and f) in vitro. f caused an increase in Km for ATP and this was reversible by subsequent R. No significant effect on Vmax was caused by the light treatments. Photoregulation of ATPase in vitro occurred only if R was given in vivo prior to extraction. The effect of R in vivo was reversible by f indicating that this also was a phytochrome response. The acid phosphatase activity was not subject to photoregulaton but its presence prevented further characterization of the K+-ATPase and its photoregulation. Phytochrome may indirectly affect K+-ATPase by affecting membrane permeability and substrate availability.
Water turnover rate, glomerular filtration rate and renal plasma and blood flow rates have been measured in individuals of the Australian desert rodent N. alexis under conditions of acute and chronic water deprivation...
详细信息
Water turnover rate, glomerular filtration rate and renal plasma and blood flow rates have been measured in individuals of the Australian desert rodent N. alexis under conditions of acute and chronic water deprivation and high nitrogen diet. When these parameters are compared with values predicted allometrically, the extreme ability of the species to conserve water is apparent only in those groups subjected to water stress. While a reversible reduction in renal function is evident upon water deprivation, the major factor in water conservation under these conditions is the renal reabsorption of water at a post-filtration stage.
Chronic ethanol vapor inhalation by rats increased hepatic microsomal aniline hydroxylase activity, increasing the turnover number and decreasing Km. Activity of ethanol-induced microsomes toward other substrates was ...
详细信息
Chronic ethanol vapor inhalation by rats increased hepatic microsomal aniline hydroxylase activity, increasing the turnover number and decreasing Km. Activity of ethanol-induced microsomes toward other substrates was also examined. Increased aniline hydroxylase activity as a result of ethanol treatment was attributed to an increase in a form of cytochrome P-450 with a high specific activity toward aniline. Since the ethanol effect on aniline hydroxylation disappeared 24 h after treatment was discontinued, a high rate of turnover of this enzyme was deduced. Dimethylsulfoxide (56 mM) produced a reverse type I spectral change in ethanol-induced but not in control microsomes. This was due to a change in the spin state of the cytochrome P-450 in these microsomes. Acetone added to the incubation produced an increased rate of aniline hydroxylation by microsomes from control and ethanol-induced rats. The difference between the rate of aniline hydroxylation by control microsomes and the rate by ethanol-induced microsomes was abolished at higher acetone concentrations.
暂无评论