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1.
The discovery of an additional step in the progression of an enzyme from the active to inactive state under the influence of temperature has led to a better match with experimental data for all enzymes that follow Michaelis–Menten kinetics, and to an increased understanding of the process. The new model of the process, the Equilibrium Model, describes an additional mechanism by which temperature affects the activity of enzymes, with implications for ecological, metabolic, structural, and applied studies of enzymes. 相似文献
2.
The effect of enzyme concentration on the H2-uptake and H2-evolving activities of the reversible hydrogenase from Thiocapsa roseopersicina was examined. In the activity range assayed by a spectrophotometric technique the apparent H2-uptake specific activity varied greatly with hydrogenase concentration. Study of H2-evolving activity measured by the H2 electrode method and compared with a gas chromatographic assay also indicated that specific activity was highly dependent on enzyme concentration. The results indicate that the widely applied hydrogenase assays give systematically erroneous specific activity values. These assays should be used only for relative measurements and the hydrogenase concentration in the reaction mixture should be kept constant. To make the data from various laboratories comparable the assay parameters should be standardized. 相似文献
3.
The genomes of two hemiascomycetous yeasts (Saccharomyces cerevisiae and Candida albicans) and one archiascomycete (Schizosaccharomyces pombe) have been completely sequenced and the genes have been annotated. In addition, the genomes of 13 more Hemiascomycetes have been partially sequenced. The amount of data thus obtained provides information on the evolutionary relationships between yeast species. In addition, the differential genetic characteristics of the microorganisms explain a number of distinctive biological traits. Gene order conservation is observed between phylogenetically close species and is lost in distantly related species, probably due to rearrangements of short regions of DNA. However, gene function is much more conserved along evolution. Compared to S. cerevisiae and S. pombe, C. albicans has a larger number of specific genes, i.e., genes not found in other organisms, a fact that can account for the biological characteristics of this pathogenic dimorphic yeast which is able to colonize a large variety of environments. 相似文献
4.
5.
近50年武威市地气温差变化趋势及影响因子 总被引:1,自引:0,他引:1
利用1961—2010年甘肃省武威市4个气象站月平均0 cm地温、气温及年日照时数、蒸发、降水、相对湿度和平均风速等观测资料,运用趋势系数法系统分析了该区域近50 a地气温差的时空分布特征,采用相关系数法和多元线性回归中的标准化回归系数分析了影响地气温差的气象因子。结果表明武威市地气温差的空间分布与地表植被、地层岩性、土层含水量等局域性因素有关,中部绿洲平原最大,北部荒漠区最小。月变化中,夏半年较大,6月最高;冬半年较小,12月最低。季节变化趋势不太一致,春夏季均呈上升趋势;秋季中北部上升,浅山区下降;冬季(除北部荒漠区外)均呈下降趋势。年和年代际变化总体呈上升趋势,中北部较显著;年平均地气温差的时间序列存在着5—7 a的准周期变化,并在2004年发生了突变。年地温、气温均呈升高趋势,年地气温差与地温、气温呈正相关。影响地气温差的主要因子是最高地温、蒸发量和降水量。地气温差与平均最高地温、平均最低气温和日照时数均呈正相关,但与蒸发、降水、相对湿度和平均风速均呈负相关。 相似文献
6.
de Pascale D Cusano AM Autore F Parrilli E di Prisco G Marino G Tutino ML 《Extremophiles : life under extreme conditions》2008,12(3):311-323
The genome of the Antarctic bacterium Pseudoalteromonas haloplanktis TAC125 was searched for the presence of genes encoding ester-hydrolysing enzymes. Amongst the others, the gene PSHAa0051
coding for a putative secreted esterase/lipase was selected. The psychrophilic gene was cloned, functionally over-expressed
in P. haloplanktis TAC125, and the recombinant product (after named PhTAC125 Lip1) was purified. PhTAC125 Lip1 was found to be associated to the outer membrane and exhibited higher enzymatic activity towards synthetic substrates
with long acyl chains. A structural model was constructed using the structure of carboxylesterase Est30 from Geobacillus stearothermophilus as template. The model covered the central part of the protein with the exceptions of PhTAC125 Lip1 N- and C-terminal regions, where the psychrophilic protein displays extra-domains. The constructed model showed
a typical α/β-hydrolase fold, and confirmed the presence of a canonical catalytic triad consisting of Ser, Asp and His. The
sequence analysis showed that PhTAC125 Lip1 is distantly related to other lipolytic enzymes, but closely related to other putative psychrophilic esterases/lipases.
The aligned proteins share common features, such as: (1) a conserved new active-site pentapeptide motif (LGG(F/L/Y)STG); (2)
the likely extra-cytoplasmic localization, (3) the absence of a typical calcium-binding pocket, and (4) the absence of a canonical
lid. These observations strongly suggest that aligned proteins constitute a novel lipase family, typical of psychrophilic
marine γ-proteobacteria, and PhTAC125 Lip1 could be considered the first characterised member of this family.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
D. de Pascale and A. M. Cusano equally contributed to the work. 相似文献
7.
Cynthia L David Valerie A Pierce Dana W Aswad Allen G Gibbs 《Comparative biochemistry and physiology. Part B, Biochemistry & molecular biology》1999,124(4):364
Urea is a protein unfolding agent that can accumulate to locally high concentrations in tissues of many organisms. We used Drosophila melanogaster to test the hypothesis that urea loading would promote formation of isoaspartate (β-carboxyl-linked aspartate), a common form of protein damage that occurs most readily in unstructured polypeptides and flexible regions of folded proteins. Ten populations of flies were tested; five control populations of urea-sensitive flies and five previously selected urea-tolerant populations. We measured the effects of urea consumption on levels of both isoaspartate and protein l-isoaspartate methyltransferase (PIMT), an enzyme believed to function in the repair or removal of isoaspartyl proteins. For both sets of populations, urea feeding for 6 days increased isoaspartyl levels by approximately 60%, supporting the idea that disruption of protein secondary and tertiary structures can accelerate the formation of isoaspartate in vivo. Urea feeding tended to increase PIMT activity in both control and urea-tolerant populations. There were no significant differences in PIMT activities or isoaspartyl levels between the control and urea-tolerant flies raised on normal or urea food. The latter findings indicate that urea tolerance evolved in the selected populations without any significant change in PIMT expression or activity. 相似文献
8.
Walter W. Ferguson 《Primates; journal of primatology》1988,29(4):535-547
The complete dentition of the common ancestor ofAustralopithecus andHomo, intermediate between that of a pongid and a hominid, is virtually unknown. The maxillary dentition (P3-M2) ofRamapithecus brevirostris
Lewis, 1934, a pongid from the Early Pliocene, and that of hominids from the Late Pliocene and Plio/Pleistocene is known. SinceR. brevirostris is probably ancestral to the hominids, a model of intermediate maxillary dentition (P3-M2) is extrapolated and described.
The model represents a hypothetical protohominid dentition. It does not conform with the teeth ofAustralopithecus, but shows greater morphological affinity to hominine dentition and to 5 myo hominids. TheHomo lineage, therefore, may go back to the Middle Pliocene. According to the normal sequence of evolution, it is most unlikely
thatAustralopithecus gave rise toHomo, but much more probable that a very early, generalizedHomo evolved into an advanced, specializedAustralopithecus. 相似文献
9.
[1-14C]glycollate was oxidised to14CO2 by peroxisomes isolated from leaves of spinach beet about 3 times as rapidly at 35°C as at 25°C; the rate was further increased with rise in temperature to a maximum at 55°C. These increases are shown to be mainly due to the increased H2O2 available to oxidise glyoxylate non-enzymically as a result of the higher temperature coefficient of glycollate oxidase activity relative to that of catalase. These results are compared with similar increases in the rate of14CO2 release between 25°C and 35°C when [1-14C]glycollate was supplied to leaf discs in light or darkness. The role of these reactions in accounting for the temperature effect on the release of photorespiratory CO2 is discussed.Abbreviations PHMS
Pyrid-2-yl--hydroxymethane sulphonate
- FMN
flavin mononucleotide 相似文献
10.
P. Q. Craufurd V. Mahalakshmi F. R. Bidinger S. Z. Mukuru J. Chantereau P. A. Omanga A. Qi E. H. Roberts R. H. Ellis R. J. Summerfield G. L. Hammer 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1999,99(5):900-911
Sorghum [Sorghum bicolor (L.) Moench] is an important cereal crop grown in a wide range of tropical and temperate environments. This study was conducted
to characterise the photothermal flowering responses of sorghum genotypes and to examine relationships between photothermal
characteristics and environment of origin in order to better understand the phenological basis of adaptation to environment
in sorghum. Twenty-four germplasm accessions and one hybrid from 24 major sorghum-growing areas were grown in a wide range
of environments varying in temperature and photoperiod in India, Kenya and Mali between 1992 and 1995. Times from sowing to
flowering (f) were recorded, and the responsiveness of 1/f to temperature and photoperiod was quantified using photothermal models. Times from sowing to flowering were accurately predicted
in a wide range of environments using a multiplicative rate photothermal model. Significant variation in the minimum time
to flower (Fm) and photoperiod sensitivity (critical photoperiod, Pc, and photoperiod-sensitivity slope, Ps) was observed among the genotypes; in contrast there was little variation in base temperature (Tb). Adaptation of sorghum to the diverse environments in which it is grown was largely determined by photoperiod sensitivity
and minimum time to flower; photoperiod sensitivity determines broad adaptation to latitude (daylength), while variation in
the minimum time to flower determines specific adaptation within smaller ranges of latitude, e.g. within the humid and sub-humid
tropics.
Received: 16 January 1999 / Accepted: 11 March 1999 相似文献
11.
E. F. Markovskaya M. I. Sysoeva E. G. Sherudilo 《Russian Journal of Developmental Biology》2008,39(5):261-268
Phenomenological responses of plants to daily short-term exposure to low hardening temperature was studied under chamber and field conditions. Experiments were carried out on cucumber (Cucumis sativus L.), barley (Hordeum vulgare L.), marigolds (Tagetes L.), and petunia (Petunia × hybrida) plants. The obtained data demonstrated a similar pattern of response in all studied plant species to different variants of exposure to low hardening temperature. The main features of plant response to daily short-term exposure to low hardening temperature include: a higher increment in cold tolerance (cf. two-or threefold increase relative to constant low hardening temperature) that peaked on day 5 (cf. day 2 at constant low hardening temperature) and was maintained for 2 weeks (cf. 3–4 days at constant low hardening temperature); a simultaneous increase in heat tolerance (cf. twofold relative to constant low hardening temperature) maintained over a long period (cf. only in the beginning of the exposure to constant low hardening temperature); a sharp drop in the subsequent cold tolerance after plant incubation in the dark (cf. a very low decrease in cold tolerance following the exposure to constant low hardening temperature); a combination of high cold tolerance and high photochemical activity of the photosynthetic apparatus (cf. a low non-photochemical quenching at constant low hardening temperature); and the capacity to increase cold tolerance in response to repeated short-term exposures to low hardening temperature in plants grown outdoors (cf. a gradual increase after repeated exposure to constant low hardening temperature). Possible mechanisms underlying the plant response to daily short-term exposure to low temperature are proposed. 相似文献
12.
Among all antibiotics tested, amoxycillin (500 ppm) completely inhibited the polygalacturonase and pectinmethylgalacturonase enzyme activity inF. oxysporum; none of the antibiotics did so inF. moniliforme. No antibiotic completely inhibited the cellulase activity in both test organisms, however, amoxycillin was better than other antibiotics in inhibiting the cellulase activity in both the organisms. 相似文献
13.
The effects of salt stress were studied on the accumulation and metabolism of proline and its correlation with Na+ and K+ content in shoots and callus tissue of four potato cultivars, viz., Agria, Kennebec (relatively salt tolerant), Diamant and Ajax (relatively salt sensitive). Na+ and proline contents increased in all cultivars under salt stress. However, K+ and protein contents decreased in response to NaCl treatments. The activities of enzymes involved in proline metabolism,
Δ1-pyrroline-5-carboxylate synthetase (P5CS) and proline dehydrogenase (ProDH) increased and decreased, respectively, in response
to elevated NaCl concentrations. The changes of P5CS and ProDH activities in more salt sensitive cultivars (Diamant, Ajax)
were more than those in the tolerant ones. Then the stimulation of synthesis in combination with a partially increase of protein
proteolysis, a decrease in proline utilization and inhibition of oxidation resulted in high proline contents in seedlings
and calli under salt stress. In callus tissue, reduced growth and cell size may be partially responsible for high proline
accumulation in response to high NaCl levels. However, although the basic proline contents in the seedlings of more salt tolerant
cultivars were higher than the sensitive ones, a clear relationship was not generally observed between accumulation of proline
and salt tolerance in potato. 相似文献
14.
Agrobacterium rhizogenes was assessed as a vehicle for transformation ofLotus corniculatus. Plants were co-transformed usingA. rhizogenes strain LBA 9402 harbouring the bacterial plasmid pRi1855 and the binary transformation vector pJit 73. pRi 1855 transfers
both TL and TR sequences, while pJit 73 encodes β-glucuronidase (GUS) and also two selectable marker genes giving resistance to the antibiotics
kanamycin and hygromycin. Three primary transformants (lines 1,6 and 12) were subjected to detailed morphological and biochemical
analysis and lines 6 and 12 were also analysed at the molecular level. Tissues of both lines 6 and 12 were resistant to hygromycin
and expressed GUS. Analysis of various tissues of each line showed a significantly lower GUS activity in line 6 than in line
12. Genetical analysis of progeny produced between control plants and lines 6 and 12 indicated that line 6 had one dose of
theuid gene while line 12 had two or more independently segregating doses of the gene. Both lines 6 and 12 contained multiple copies
of TL-DNA, while only line 6 was TR positive. In the progeny of lines 6 and 12 there was no evidence for linkage of TL-DNA withuid, while in the progeny of line 6, TR-DNA was under-represented. GUS-positive progeny which were free of both TL and TR sequences were identified from both lines. 相似文献
15.
Storbeck S Saha S Krausze J Klink BU Heinz DW Layer G 《The Journal of biological chemistry》2011,286(30):26754-26767
During the biosynthesis of heme d1, the essential cofactor of cytochrome cd1 nitrite reductase, the NirE protein catalyzes the methylation of uroporphyrinogen III to precorrin-2 using S-adenosyl-l-methionine (SAM) as the methyl group donor. The crystal structure of Pseudomonas aeruginosa NirE in complex with its substrate uroporphyrinogen III and the reaction by-product S-adenosyl-l-homocysteine (SAH) was solved to 2.0 Å resolution. This represents the first enzyme-substrate complex structure for a SAM-dependent uroporphyrinogen III methyltransferase. The large substrate binds on top of the SAH in a “puckered” conformation in which the two pyrrole rings facing each other point into the same direction either upward or downward. Three arginine residues, a histidine, and a methionine are involved in the coordination of uroporphyrinogen III. Through site-directed mutagenesis of the nirE gene and biochemical characterization of the corresponding NirE variants the amino acid residues Arg-111, Glu-114, and Arg-149 were identified to be involved in NirE catalysis. Based on our structural and biochemical findings, we propose a potential catalytic mechanism for NirE in which the methyl transfer reaction is initiated by an arginine catalyzed proton abstraction from the C-20 position of the substrate. 相似文献
16.
The effect of temperature on the development time and brood size of diaptomus pallidus herrick 总被引:1,自引:1,他引:0
David M. Kamps 《Hydrobiologia》1978,61(1):75-80
Diaptomus pallidus individuals were raised in the laboratory at three temperatures (15, 20, and 25°C) and fed an alfalfa and trout-food diet ad libitum. Data were taken on the development times of the egg, naupliar, and each copepodid stage and the brood sizes of field animals acclimated to the test conditions.The results indicated D. pallidus does not have a temperature range over which its development rate is nearly constant as earlier reported. Rather, the development rate is temperature dependent within the experimental range. Broods produced at 20°C and 25°C were significantly smaller than those produced at 15°C but not significantly different from each other. 相似文献
17.
Patricia Molina Ronald M.A. Knegtel Bruce A. Macher 《Biochimica et Biophysica Acta (BBA)/General Subjects》2007
Bovine α1,3galactosyltransferase (α1,3GalT) transfers galactose from UDP-α-galactose to terminal β-linked galactosyl residues with retention of configuration of the incoming galactose residue. The epitope synthesized has been shown to be critical for xenotransplantation. According to a proposed double-displacement reaction mechanism, glutamate-317 (E317) is thought to be the catalytic nucleophile. The proposed catalytic role of E317 involves an initial nucleophilic attack with inversion of configuration and formation of a covalent sugar–enzyme intermediate between E317 and galactose from the donor substrate, followed by a second nucleophilic attack performed by the acceptor substrate with a second inversion of configuration. To determine whether E317 of α1,3GalT is critical for enzyme activity, site-directed mutagenesis was used to substitute alanine, aspartic acid, cysteine and histidine for E317. If the proposed reaction mechanism for the α1,3GalT enzyme is correct, E317D and E317H would produce active enzymes since they can act as nucleophiles. The non-conservative mutation E317A and conservative mutation E317C are predicted to produce inactive or very low activity enzymes since the E317A mutant cannot engage in a nucleophilic attack, and the E317C mutant would trap the galactose residue. The results obtained demonstrate that E317D and E317H mutants retained activity, albeit significantly less than the wild-type enzyme. Additionally, both E317A and E317C mutant also retained enzyme activity, suggesting that E317 is not the catalytic nucleophile proposed in the double-displacement mechanism. Therefore, either a different amino acid may act as the catalytic nucleophile or the reaction must proceed by a different mechanism. 相似文献
18.
Ma Lin Li Beatrice Panterne Jean-Pierre Levesque Antoinette Hatzfeld Jacques Hatzfeld 《In vitro cellular & developmental biology. Animal》1992,28(6):459-460
Summary Leupeptin, a thiol- and serine-proteinase inhibitor of low molecular weight, quickly enters viable cells. This property has
been used to protect cells during thawing against intracellular proteolytic activities released by injured lysosomes. The
bone marrow nucleated cells were frozen without rate-controlled freezing devices. Concentrations ranging from 0.1 to 1μM of leupeptin allow to recover 87% of the most immature multipotent bone marrow progenitors which can develop in vitro into
large multilineage colonies, instead of 58% recovery without leupeptin. The protective effect of leupeptin is particularly
useful to freeze cells difficult to cryopreserve or when freezing-control equipments are not available. 相似文献
19.
Sudha S. Ambedkar Bhagwant S. Deshpande Vayalombron K. Sudhakaran Jaiprakash G. Shewale 《Journal of industrial microbiology & biotechnology》1991,7(3):209-214
Summary
Beijerinckia indica var.penicillanicum mutant UREMS-5, producing 168% more penicillin V acylase, was obtained by successive treatment with UV, -irradiation and ethylmethane sulfonate. Penicillin V acylase production by the mutant strain was resistant to catabolite repression by glucose. Incorporation of glucose, sodium glutamate and vegetable oils in the medium enhanced enzyme production. The maximum specific production of penicillin V acylase was 244 IU/g dry weight of cells. Effect of solvents on hydrolysis of penicillin V by soluble penicillin V acylase and whole cells was studied. Methylene chloride, chloroform and carbon tetrachloride significantly stimulated the rate of penicillin V hydrolysis by whole cells. 相似文献
20.
Aquatic invertebrates are usually larger at maturity when water temperatures are lower. For the freshwater cladoceran Daphnia, it has been suggested that a threshold size must be attained to initiate maturation, which results two instars later in the deposition of eggs into the brood chamber. This threshold size is believed to temperature on maturation threshold body-length in Daphnia magna. Daphnids were raised from birth to maturity under three constant-temperature regimes (12°C, 16°C, 22°C), and two food-level conditions. Animals were measured daily, and a body-length based maturation threshold determined for each individual. We demonstrate that mean maturation threshold length is negatively correlated with ambient water temperature. Further, daphnids with a larger threshold length tended to be larger at maturity. A maturation threshold linked to body length suggests that reduced variation in size at maturity is adaptive, even at the cost of additional variation in instar number or age at maturity. 相似文献