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1.
The 20S proteasome of eukaryotic cells has at least three distinct peptidase activities (trypsin-like, chymotrypsin-like and peptidylglutamylpeptide (PGP) hydrolase activities). These peptidases are latent and require appropriate activators. SDS has been widely used as an activator of these peptidases, but the mechanism of its activation remains unresolved. In this study, we investigated the kinetics of the SDS-activated hydrolysis of the above three types of peptidase of the 20S proteasome purified from Xenopus oocytes. When the reaction was started by simultaneous adding both SDS and substrate, maximal rates of hydrolysis were reached after appreciable lag phases with the trypsin-type substrate [t-butyloxycarbonylLeu-Arg-Arg-4-methylcoumaryl-7-amide (Boc-LRR-MCA)], but no such lag phases were observed with the chymotrypsin-type and PGP hydrolase-type substrates [succinyl-Leu-Leu-Val-Tyr-4-methylcoumaryl-7-amide (Suc-LLVY-MCA), and benzyloxycarbonyl-Leu-Leu-Glu-2-naphthylamide (Cbz-LLE-2NA), respectively]. Similarly, changes in the hydrolysis rate to a reduced level upon dilution of SDS occurred after an appreciable lag phase again in the trypsin-like peptidase, but not in the other types. The lag phase characteristic of the trypsin-like peptidase was dependent on the substrate concentration. Thus, the lag phase was less discernible at very low concentrations of the substrate (e.g. at concentrations in the order of 1/100 of the Km value), but became more conspicuous with the increases in the substrate concentration. This lag phase also vanished upon preincubation of the activator (SDS) for a short period of 5 sec. These results suggest that the formation of the enzyme-substrate complex in the trypsin-like reaction induces a conformational change in the enzyme which makes the SDS activator site(s) in an occluded form, reducing the rates of SDS binding and dissociation. 相似文献
2.
Hatanaka Akikazu; Kajiwara Tadahiko; Sekiya Jiro; Imoto Masaya; Inouye Satoshi 《Plant & cell physiology》1982,23(1):91-99
Isolated tea chloroplasts utilized linoleic acid, linolenicacid and their 13-hydroperoxides as substrates for volatileC6-aldehyde formation. Optimal pH values for oxygen uptake,hydroperoxide lyase and the overall reaction from C18-fattyacids to C6-aldehydes were 6.3, 7.0 and 6.3, respectively. Methyllinoleate, linoleyl alcohol and -linolenic acid were poor substratesfor the overall reaction, but linoleic and linolenic acids weregood substrates. The 13-hydroperoxides of the above fatty acidsand alcohol also showed substrate specificity similar to thatof fatty acids. Oxygen uptakes (relative Vmax) with methyl linoleate,linoleyl alcohol, linolenic acid, -linolenic acid and arachidonicacid were comparable to or higher than that with linoleic acid.In winter leaves, the activity for C6-aldehyde formation fromC18-fatty acids was raduced to almost zero. This was due tothe reduction in oxygenation. The findings presented here provideevidence for the involvement of lipoxygenase and hydroperoxidelyase in C6-aldehyde formation in isolated chloroplasts. (Received July 11, 1981; Accepted November 5, 1981) 相似文献
3.
Identification and characterization of three different subpopulations of the Drosophila multicatalytic proteinase (proteasome) 总被引:5,自引:0,他引:5
In Drosophila melanogaster the population of proteasome particles consists of three distinct subclasses. By fractionation of a 40,000 x g supernatant of Drosophila homogenate on a DEAE-Sephacel column, proteasome particles which elute at salt concentrations of 200, 300, and 500 mM KAc can be separated. The proteasomes of all three subfractions sediment at 19 S in sucrose gradients and are shown by two-dimensional gel electrophoretic analysis to possess the same protein content. They differ, however, with respect to their specific proteolytic activity against the substrates benzoyl-Val-Gly-Arg-4-methylcoumaryl-7-amide, succinyl-Leu-Leu-Val-Tyr-4-methylcoumaryl-7-amide, and succinyl-Ala-Ala-Phe-4-methylcoumaryl-7-amide and the degree to which their hydrolytic activity can be enhanced by the addition of 30-110 microM sodium dodecyl sulfate (SDS). Our data show that the 200 mM proteasome fraction exhibits the lowest basal specific proteolytic activity but can be stimulated most by SDS. The 300 and 500 mM proteasome subfractions, on the other hand possess considerably higher but similar basal specific proteolytic activity. Of these only the proteolytic activity of the 300 mM subfraction against the substrates benzoyl-Val-Gly-Arg-4-methylcoumaryl-7-amide and succinyl-Leu-Leu-Val-Tyr-4-methylcoumaryl-7-amide can be enhanced by SDS. Our data raise the possibility that the different subpopulations reflect structural differences between the proteasome particles, which in turn may result in different in vivo substrate specificities of the proteasome subpopulations. 相似文献
4.
Leaf alcohol (cis-3-hexenol) and leaf aldehyde (trans-2-hexenal)are responsible for the green odor in leaves and fruits. cis-3-Hexenal,a precursor of cis-3-hexenol and trans-2-hexenal, was producedfrom linolenic acid by a homogenate of Farfugium japonicum (Japanesesilver) leaves. n-Hexanal was produced from linoleic acid bya homogenate of the leaves. The enzyme system catalyzing formationof C6-aldehydes from linolenic and linoleic acids was localizedin chloroplast lamellae, and required oxygen for reaction. C18-unsaturatedfatty acids such as linolenic acid, linoleic acid and -linolenicacid, which have carboxyl groups and cis-1, cis-4-pentadienesystems including a double bond at C-12, acted as substrates,and C6-aldehydes (cis-3-hexenal or n-hexanal), but not C9-aldehydes,were produced from them. The properties of the enzyme systemin chloroplasts were as follows: optimal pH 7.0; stable at pH5 to 7; thermolabile and no activity at 50?C. These propertieswere very similar to those of tea chloroplasts. The enzyme systemcould be solubilized from chloroplasts by 2% Triton X-100, butwas very unstable in solubilized form. (Received July 9, 1976; ) 相似文献
5.
When tea leaves were homogenized and incubated, the volatileC6-compounds hexanal, cis-3-hexenal, cis-3-hexenol and trans-2-hexenalwere formed much more by summer leaves than by winter leavesof tea plants (Camellia sinensis). The enzymes lipolytic acylhydrolase (LAH), lipoxygenase, fatty acid hydroperoxide lyase(HPO lyase) and alcohol dehydrogenase (ADH) and an isomerizationfactor were responsible for the sequential reactions of C6-compoundformation from linoleic and linolenic acids in tea leaf lipids,and there were seasonal changes in their activities. The tealeaf enzymes were of 3 types: LAH and lipoxygenase, which hadhigh activities in summer leaves and low activities in winterleaves; ADH, which had low activity in summer leaves and highactivity in winter ones; and HPO lyase and the isomerizationfactor, which did not seem to have any effect on the rate ofC6-compound formation throughout the year. Changes in enzymeactivities were induced by shifts in the environmental air temperaturerather than by the age of the leaves. The combined activitiesof these enzymes determined the amounts and compositions ofthe volatile C6-compounds formed, which are the factors thatcontrol the quality of the raw leaves processed for green tea. (Received October 6, 1983; Accepted December 20, 1983) 相似文献
6.
A strong correlation between the photosynthetic parameters Jmaxand Vcmax was found by Wullschleger (1993) in a survey of 109plant species. Measurements were made at various leaf temperatures,but the temperature dependence of Jmax and Vcmax differ. Oncevalues for Jmax and Vcmax in Wullschleger's analysis were adjustedto a common temperature, using an equation for the temperaturedependence of these parameters, the slope of the linear regressionfor Jmax versus Vcmax forced through the origin increased from1.97 to 2.68, and r2 increased from 0.79 to 0.87. Key words: Temperature, photosynthesis parameters 相似文献
7.
Influence of myosin isoforms on contractile properties of intact muscle fibers from Rana pipiens 总被引:3,自引:0,他引:3
Lutz GJ Sirsi SR Shapard-Palmer SA Bremner SN Lieber RL 《American journal of physiology. Cell physiology》2002,282(4):C835-C844
The myosin heavy chain (MHC) andmyosin light chain (MLC) isoforms in skeletal muscle of Ranapipiens have been well characterized. We measured theforce-velocity (F-V) properties of single intact fast-twitchfibers from R. pipiens that contained MHC types 1 or 2 (MHC1or MHC2) or coexpressed MHC1 and MHC2 isoforms. Velocities weremeasured between two surface markers that spanned most of the fiberlength. MHC and MLC isoform content was quantified after mechanicsanalysis by SDS-PAGE. Maximal shortening velocity(Vmax) and velocity at half-maximal tension(VP 50) increased with percentage of MHC1(%MHC1). Maximal specific tension (Po/CSA, wherePo is isometric tension and CSA is fiber cross-sectional area) and maximal mechanical power (Wmax) alsoincreased with %MHC1. MHC concentration was not significantlycorrelated with %MHC1, indicating that the influence of %MHC1 onPo/CSA and Wmax was due to intrinsicdifferences between MHC isoforms and not to concentration. TheMLC3-to-MLC1 ratio was not significantly correlated withVmax, VP 50,Po/CSA, or Wmax. These data demonstrate the powerful relationship between MHC isoforms and F-V properties of the two most common R. pipiensfiber types. 相似文献
8.
The desaturation of fatty acids in the monogalactosyl diacylglycerolupon a downward shift in temperature was studied under variousconditions in Anabaena variabilis. The following conclusionsare drawn from the experimental results. (1) The desaturationof palmitic to palmitoleic acids after the temperature shiftfrom 38 to 22°C occurs in the dark as well as in the light.The desaturations of oleic to linoleic and of linoleic to linolenicacids after the temperature shift are stimulated by illumination.(2) The C16 and C18 acids are desaturated to different degreesdepending on the magnitude of the temperature shift. (3) Thedesaturations require molecular oxygen. (4) Syntheses of RNAand proteins are involved in the mechanism for the temperatureshift-induced desaturation of fatty acids. (Received May 27, 1981; Accepted July 7, 1981) 相似文献
9.
Effects of fatty acids on BK channels in GH(3) cells 总被引:6,自引:0,他引:6
Denson DD Wang X Worrell RT Eaton DC 《American journal of physiology. Cell physiology》2000,279(4):C1211-C1219
Ca2+-activated K+ (BK) channels inGH3 cells are activated by arachidonic acid (AA). Becausecytosolic phospholipase A2 can produce other unsaturatedfree fatty acids (FFA), we examined the effects of FFA on BK channelsin excised patches. Control recordings were made at several holdingpotentials. The desired FFA was added to the bath solution, and thevoltage paradigm was repeated. AA increased the activity of BK channelsby 3.6 ± 1.6-fold. The cis FFA, palmitoleic, oleic,linoleic, linolenic, eicosapentaenoic, and the triple bond analog ofAA, eicosatetraynoic acid, all increased BK channel activity, whereasstearic (saturated) or the trans isomers elaidic,linolelaidic, and linolenelaidic had no effect. The cisunsaturated FFA shifted the open probability vs. voltage relationshipsto the left without a change in slope, suggesting no change in thesensitivity of the voltage sensor. Measurements of membrane fluidityshowed no correlation between the change of membrane fluidity and thechange in BK channel activation. In addition, AA effects on BK channelswere unaffected in the presence of N-acetylcysteine.Arachidonyl-CoA, a membrane impermeable analog of AA, activateschannels when applied to the cytosolic surface of excised patches,suggesting an effect of FFAs from the cytosolic surface of BK channels.Our data imply a direct interaction between cis FFA and theBK channel protein. 相似文献
10.
MATTSSON M; JOHANSSON E; LUNDBORG T.; LARSSON M.; LARSSON C.-M. 《Journal of experimental botany》1991,42(2):197-205
Growth and nitrate uptake kinetics in vegetatively growing barley(Hordeum vulgare L., cvs Laevigatum, Golf, and Mette) were investigatedin solution culture under long-term limitations of externalnitrogen availability. Nitrate was fed to the cultures at relativeaddition rates (RA) ranging from 0.02 to 0.2 d1. Therelative growth rate (RG, calculated for total plant dry weight)correlated well with RA in the range 0.02 to 0.07 d1.In the RA range from 0.07 to 0.2 d1 RG continued to increase,but an increasing fraction of nitrogen, added and absorbed,was apparently stored rather than used for structural growth.The RG of the roots was less affected by RA. Vmax, for net nitrateuptake increased with RA up to 0.11 d1, but decreasedat higher RA. The decline in Vmax coincided with a build-upof nitrate stores in both roots and shoots. Vmax, expressedper unit nitrogen in the plants (the relative Vmax, was higherthan required for maintenance of growth (up to 30-fold) at lowRA, whereas at higher RA the relative Vmax decreased. Kineticpredictions of steady-state external nitrate concentrationsduring N-limited growth ranged from 0.2 to 5.0 mmol m3over the RG range 0.02 to 0.11 d1. It is suggested thatthe nitrate uptake system is not under specific regulation atlow RA, but co-ordinated with root protein synthesis and growthin general. At RA higher than 0.11 d1, however, specificregulation of nitrate uptake, possibly via root nitrate pools,become important. The three cultivars showed very similar growthand nitrate uptake characteristics. Key words: Barley, growth, nitrogen limitation, nitrate uptake, kinetics 相似文献
11.
Potent block of inactivation-deficient Na+ channels by n-3 polyunsaturated fatty acids 总被引:1,自引:0,他引:1
Xiao YF Ma L Wang SY Josephson ME Wang GK Morgan JP Leaf A 《American journal of physiology. Cell physiology》2006,290(2):C362-C370
A voltage-gated, small, persistent Na+ current (INa) has been shown in mammalian cardiomyocytes. Hypoxia potentiates the persistent INa that may cause arrhythmias. In the present study, we investigated the effects of n-3 polyunsaturated fatty acids (PUFAs) on INa in HEK-293t cells transfected with an inactivation-deficient mutant (L409C/A410W) of the -subunit (hH1) of human cardiac Na+ channels (hNav1.5) plus 1-subunits. Extracellular application of 5 µM eicosapentaenoic acid (EPA; C20:5n-3) significantly inhibited INa. The late portion of INa (INa late, measured near the end of each pulse) was almost completely suppressed. INa returned to the pretreated level after washout of EPA. The inhibitory effect of EPA on INa was concentration dependent, with IC50 values of 4.0 ± 0.4 µM for INa peak (INa peak) and 0.9 ± 0.1 µM for INa late. EPA shifted the steady-state inactivation of INa peak by 19 mV in the hyperpolarizing direction. EPA accelerated the process of resting inactivation of the mutant channel and delayed the recovery of the mutated Na+ channel from resting inactivation. Other polyunsaturated fatty acids, docosahexaenoic acid, linolenic acid, arachidonic acid, and linoleic acid, all at 5 µM concentration, also significantly inhibited INa. In contrast, the monounsaturated fatty acid oleic acid or the saturated fatty acids stearic acid and palmitic acid at 5 µM concentration had no effect on INa. Our data demonstrate that the double mutations at the 409 and 410 sites in the D1S6 region of hH1 induce inactivation-deficient INa and that n-3 PUFAs inhibit mutant INa. human cardiac sodium channel 相似文献
12.
The chemomechanicalcoupling mechanism in striated muscle contraction was examined bychanging the nucleotide substrate from ATP to CTP. Maximum shorteningvelocity [extrapolation to zero force from force-velocity relation(Vmax) andslope of slack test plots (V0)], maximumisometric force (Po), power, andthe curvature of the force-velocity curve[a/Po(dimensionless parameter inversely related to the curvature)] weredetermined during maximumCa2+-activated isotoniccontractions of fibers from fast rabbit psoas and slow rat soleusmuscles by using 0.2 mM MgATP, 4 mM MgATP, 4 mM MgCTP, or 10 mM MgCTPas the nucleotide substrate. In addition to a decrease in the maximumCa2+-activated force in both fibertypes, a change from 4 mM ATP to 10 mM CTP resulted in a decrease inVmax in psoasfibers from 3.26 to 1.87 muscle length/s. In soleus fibers,Vmax was reduced from 1.94 to 0.90 muscle length/s by this change in nucleotide. Surprisingly, peak power was unaffected in either fiber type by thechange in nucleotide as the result of a three- to fourfold decrease inthe curvature of the force-velocity relationship. The results areinterpreted in terms of the Huxley model of muscle contraction as anincrease in f1and g1 coupled toa decrease in g2(where f1 is therate of cross-bridge attachment and g1 andg2 are rates ofdetachment) when CTP replaces ATP. This adequately accounts for theobserved changes in Po,a/Po,and Vmax.However, the two-state Huxley model does not explicitly reveal thecross-bridge transitions that determine curvature of the force-velocityrelationship. We hypothesize that a nucleotide-sensitive transitionamong strong-binding cross-bridge states followingPi release, but before the release of the nucleotide diphosphate, underlies the alterations ina/Po reported here. 相似文献
13.
Suppression of the High Affinity Phosphate Uptake System: A Mechanism of Arsenate Tolerance in Holcus lanatus L. 总被引:19,自引:0,他引:19
In Holcus lanatus L. phosphate and arsenate are taken up bythe same transport system. Short-term uptake kinetics of thehigh affinity arsenate transport system were determined in excisedroots of arsenate-tolerant and non-tolerant genotypes. In tolerantplants the Vmax of ion uptake in plants grown in phosphate-freemedia was decreased compared to non-tolerant plants, and theaffinity of the uptake system was lower than in the non-tolerantplants. Both the reduction in Vmax and the increase in Km ledto reduced arsenate influx into tolerant roots. When the twogenotypes were grown in nutrient solution containing high levelsof phosphate, there was little change in the uptake kineticsin tolerant plants. In non-tolerant plants, however, there wasa marked decrease in the Vmax to the level of the tolerant plantsbut with little change in the Km. This suggests that the lowrate of arsenate uptake over a wide range of differing rootphosphate status is due to loss of induction of the synthesisof the arsenate (phosphate) carrier. Key words: Arsenate, Holcus lanatus L., phosphate uptake, tolerance mechanisms, uptake mechanisms 相似文献
14.
Metabolism of n-3 polyunsaturated fatty acids and modification of phospholipids in cultured rabbit aortic smooth muscle cells 总被引:1,自引:0,他引:1
N Morisaki T Kanzaki Y Fujiyama I Osawa K Shirai N Matsuoka Y Saito S Yoshida 《Journal of lipid research》1985,26(8):930-939
The metabolism of the linolenic acid family (n-3) of fatty acids, e.g., linolenic, eicosapentaenoic, and docosahexaenoic acids, in cultured smooth muscle cells from rabbit aorta was compared to the metabolism of linoleic and arachidonic acids. There was a time-dependent uptake of these fatty acids into cells for 16 hr (arachidonic greater than docosahexaenoic, linoleic, eicosapentaenoic greater than linolenic), and the acids were incorporated mainly into phospholipids and triglycerides. Eicosapentaenoic and arachidonic acids were incorporated more into phosphatidylethanolamine and phosphatidylinositol plus phosphatidylserine and less into phosphatidylcholine than linolenic and linoleic acids. Docosahexaenoic acid was incorporated into phosphatidylethanolamine more than linolenic and linoleic acids and into phosphatidylinositol plus phosphatidylserine less than eicosapentaenoic and arachidonic acids. Added linolenic acid accumulated mainly in phosphatidylcholine and did not decrease the arachidonic acid content of any phospholipid subfraction. Elongation-desaturation metabolites of linoleic acid did not accumulate. Cells treated with eicosapentaenoic acid accumulated both eicosapentaenoic and docosapentaenoic acids mainly in phosphatidylethanolamine and the arachidonic acid content was decreased. Added docosahexaenoic acid accumulated mainly in phosphatidylethanolamine and decreased the content of both arachidonic and oleic acids. The following conclusions are drawn from these results. The three n-3 fatty acids are utilized differently in phospholipids. The arachidonic acid content of phospholipids is reduced by eicosapentaenoic and docosahexaenoic acids, but not by linolenic acid. Smooth muscle cells have little or no desaturase activity, but have significant elongation activity for polyunsaturated fatty acids. 相似文献
15.
Nutrient-limited growth rates: quantitative benefits of stress responses and some aspects of regulation 总被引:3,自引:0,他引:3
Young sunflower plants (Helianthus annuus L.) under stress oflow nitrate or phosphate availability exhibited increases inroot: shoot ratio and in kinetic parameters for uptake. Theyshowed no significant changes in photosynthetic utilizationof either nutrient. Increases in root: shoot ratio were achievedby early and persistent suppression of shoot growth, but notroot growth. Affinity for phosphate uptake, 1/Km(P), increasedwith phosphate stress, as did affinity for nitrate uptake, 1/Km(N),with nitrate stress. Maximal uptake rate, Vmax, for phosphateuptake increased with phosphorus stress; Vmax for nitrate didnot increase with nitrogen stress. Phosphate Vmax was relatedstrongly to root nutrient status. Decreases in Vmax with plantage were not well explained by changes in age structure of roots.Estimated benefits of acclimatory changes in root: shoot ratioand uptake kinetics ranged up to 2-fold increases in relativegrowth rate, RGR. The relation of RGR to uptake physiology followedpredictions of functional balance moderately well, with somesystematic deviations. Analyses of RGR using growth models implyno significant growth benefit from regulating Vmax, specifically,not from down-regulating it at high nutrient availability. Quantitativebenefits of increases in root: shoot ratio and uptake parametersare predicted to be quite small under common conditions whereinnutrient concentrations are significantly depleted by uptake.The root: shoot response is estimated to confer the smallestbenefit under non-depleting conditions and the largest benefitunder depleting conditions. Even then, the absolute benefitis predicted to be small, possibly excepting the case of heterogeneoussoils. Depleting and non-depleting conditions are addressedwith very different experimental techniques. We note that atheoretical framework is lacking that spans both these cases,other than purely numerical formulations that are not readilyinterpreted. Key words: Nutrient stress, nutrient uptake, nutrient use efficiency, relative growth rate, Helianthus annuus 相似文献
16.
Long-chain acyl coenzyme A (CoA) synthetase in homogenates and microsomes from rat brain gray and white matter was studied. The formation of the thioesters of CoA was studied upon addition of [1-14C]-labeled fatty acids. The maximal activities were seen with linoleic acid, followed by arachidonic, palmitic, and docosahexaenoic acids in both gray and white matter homogenates and microsomes. The specific activities in microsomes were 3–5 times higher than in homogenates. The presence of Triton X-100 in the assay system enhanced the activity of long-chain acyl CoA synthetase in homogenates. The effect was more pronounced in palmitic and docosahexaenoic acid activation. The apparentK
m values andV
max values for palmitic and docosahexaenoic acids were much lower than for linoleic and arachidonic acids. The presence of Triton X-100 in the medium caused a definite decrease in the apparentK
m and Vmax values for all the fatty acid except palmitic acid in which case the reverse was true. There were no significant differences observed in the kinetic measurements between gray and white matter microsomes. These findings are similar to those resulting from the known interference of Triton X-100 in the measurement of kinetic variables of long-chain acyl CoA synthetase of liver microsomes. In this work, no correlation was observed between the fatty acid composition of gray and white matter and the capacity of these tissues for the activation of different fatty acids. 相似文献
17.
淡色库蚊中抗性相关羧酸酯酶的纯化及其生化性质 总被引:3,自引:1,他引:2
在库蚊Culex pipiens品系中,非专一性酯酶活性的升高是对有机磷杀虫剂产生抗性的重要机理之一。应用SDS/PAGE,比较淡色库蚊Culex pipiens pallens抗敌百虫品系(RD)、敏感型品系(S)和抗苄呋菊酯品系(PY)中可溶性总蛋白质带型,显示RD中含有一条特异蛋白带,其它两个品系中未检出。在RD成虫匀浆液总蛋白中含量高达2.1%。分子量测定为66 kD。应用柱层析法分离得到了较纯的纯品。以α-NA为底物测得Km=64.1 mmol/L,Vmax=249.8 mmol/(L·mg·min)。与羧酸酯酶相比较:其Km值小于已报道的抗性品系及非抗性品系A-酯酶和B-酯酶。Vmax值比已报道抗性品系A-酯酶低,比B-酯酶高。较高浓度的敌百虫并不能抑制其酶活,属于A-酯酶。在昆虫体内可能主要通过结合隔离作用(sequestration)提高昆虫对有机磷的耐受性,对有机磷杀虫剂水解作用的可能性也不能排除。 相似文献
18.
GROENHOF ANDREW C.; SMIRNOFF NICHOLAS; BRYANT JOHN A. 《Journal of experimental botany》1988,39(3):353-361
ABSRACT: Groenhof, A. C, Smirnoff, N. and Bryant, J. A. 1988. Enzymicactivities associated with the ability of aerial and submergedforms of Littorella uniflora (L.) Aschers to perform CAM.J.exp. Bot. 39: 353-361. The submerged form of Littorella uniflora shows a full CAM modeof photosynthesis as shown by diel acid fluctuations and elevatedactivities (in comparison to non-submerged leaves) of the enzymesphosphoenolpyruvate carboxylase (PEPC) and NADP-malic enzyme.Non-submerged plants exhibit no diel fluctuations of acidityand no changes in activity of NADP-malic enzyme or PEPC. PEPCactivity is low and NADP-malic enzyme is not detectable. Furthercharacterization of PEPC extracted from submerged plants duringthe light and dark periods of a diel cycle shows that the enzymeextracted in the dark is more active. In addition, the enzymeshows a decrease in Km (PEP) and an increase in Vmax in thepresence of glucose-6-phosphate, whilst in the presence of malateKm (PEP) is increased and Vmax decreased; this response to malateis only observed in the light and at pH 7.2. Molecular weightdeterminations using a Sephacryl S-300 column show that theenzyme extracted from plants during the dark period has an apparentmol. wt. of 375 KDa and the enzyme extracted from plants duringthe light period has an apparent mol. wt. of 307 KDa. Key words: Littorella uniflora (shoreweed), Crassulacean acid metabolism, PEP carboxylase, malic enzyme 相似文献
19.
YANIV ZOHARA; RANEN CARMELLA; LEVY A.; PALEVITCH D. 《Journal of experimental botany》1989,40(5):609-613
The oil content and yield of evening primrose (Oenothera lamarckianaL.) seeds decreased significantly at high temperatures (32 ?C)compared with lower ones (25 ?C and below), under controlledgrowing conditions. Moreover, the fatty acid composition ofthe seed oils was also affected by the temperature regime. Higheroleic acid levels and lower linoleic and -linolenic acid (GLA)levels were characteristic of the seeds developed at highertemperatures. The opposite trend was observed at lower temperatures.In field experiments, seeds of O. lamarckiana plants sown inautumn contained lower oleic acid levels, and higher linoleicacid and GLA levels than seeds of spring plantings. This effectwas also demonstrated for seeds developed on the same stem inflorescenceunder increasing temperatures during the season in the field.Changes in fatty acid composition during various stages of seeddevelopment were observed. Key words: Evening primrose, oil, fatty acids, Oenothera spp., gamma linolenic acid 相似文献
20.
Seed triglycerides of Andropogon gayanus contained 17 fatty acid moieties, principally palmitic, oleic and linoleic acids. These were distributed in an essentially random manner amongst the triglycerides to form the following main types: POL, PLL, OOL, LLO and LLL. Triglycerides decreased during both light and dark germination but there was no evidence for selective hydrolysis. Free fatty acids appear to be derived from triglyceride hydrolysis but the free and triglyceride fatty acid composition differed. Less palmitic, oleic and linoleic acids and more stearic, linolenic and C20-acids were found in the free state than combined in the triglycerides. Free fatty acids did not accumulate during germination. 相似文献