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1.
Qingfeng Chen Corey S. Westfall Leslie M. Hicks Shiping Wang Joseph M. Jez 《The Journal of biological chemistry》2010,285(39):29780-29786
The GH3 family of acyl-acid-amido synthetases catalyze the ATP-dependent formation of amino acid conjugates to modulate levels of active plant hormones, including auxins and jasmonates. Initial biochemical studies of various GH3s show that these enzymes group into three families based on sequence relationships and acyl-acid substrate preference (I, jasmonate-conjugating; II, auxin- and salicylic acid-conjugating; III, benzoate-conjugating); however, little is known about the kinetic and chemical mechanisms of these enzymes. Here we use GH3-8 from Oryza sativa (rice; OsGH3-8), which functions as an indole-acetic acid (IAA)-amido synthetase, for detailed mechanistic studies. Steady-state kinetic analysis shows that the OsGH3-8 requires either Mg2+ or Mn2+ for maximal activity and is specific for aspartate but accepts asparagine as a substrate with a 45-fold decrease in catalytic efficiency and accepts other auxin analogs, including phenyl-acetic acid, indole butyric acid, and naphthalene-acetic acid, as acyl-acid substrates with 1.4–9-fold reductions in kcat/Km relative to IAA. Initial velocity and product inhibition studies indicate that the enzyme uses a Bi Uni Uni Bi Ping Pong reaction sequence. In the first half-reaction, ATP binds first followed by IAA. Next, formation of an adenylated IAA intermediate results in release of pyrophosphate. The second half-reaction begins with binding of aspartate, which reacts with the adenylated intermediate to release IAA-Asp and AMP. Formation of a catalytically competent adenylated-IAA reaction intermediate was confirmed by mass spectrometry. These mechanistic studies provide insight on the reaction catalyzed by the GH3 family of enzymes to modulate plant hormone action. 相似文献
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In this paper we report the observation of a rapidly developed vertebrate symbiosis involving ectoparasite cleaning by a native corvid of northern Australia, the Torresian crow Corvus orru , on a recently introduced bovid ungulate, the banteng Bos javanicus . Facultative symbioses benefiting both participants (mutualisms) between birds and mammals appear to be rare, despite the apparent advantages obtained by the participants (ecto-parasite removal from the host and food provision to the cleaner). On three separate dates we observed a total of four C. orru individuals eliciting facilitation behaviours by a total of ten female banteng to assist in the removal of ectoparasites. Our observations document the first-known incidence of facultative cleaning behaviour by a native bird species on a non-native, wild vertebrate that has developed in approximately 150 years since the banteng's introduction to Australia. 相似文献
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Efficient methods for attachment of thiol specific probes to the 3''-ends of synthetic oligodeoxyribonucleotides. 总被引:10,自引:7,他引:3
Methodology is described for the synthesis of DNA oligomers containing a free 3'-thiol group which can be selectively crosslinked with a wide variety of probes. This chemistry is compatible with both phosphotriester and phosphoramidite solid phase chemistry. Moreover, the sulphydryl group is introduced into the 3'-nucleoside solid support linkage prior to oligonucleotide synthesis. Consequently, no additional coupling steps are required after oligonucleotide synthesis, and isolation of the 3'-thiol oligonucleotide requires only one additional deprotection step. Cross-linking of the thiol-containing oligonucleotide to a fluorescent probe was carried out with high selectivity, in high yield, and under mild conditions. 相似文献
6.
Ion channel expression by white matter glia: the type-1 astrocyte. 总被引:10,自引:0,他引:10
We describe the electrophysiological properties of acutely isolated type-1 astrocytes using a new "tissue print" dissociation procedure. Because the enzymes used did not destroy or modify the ion channels, and the cells retained many processes, the properties may reflect those in vivo. The types of ion channels in type-1 astrocytes changed rapidly during the first 10 postnatal days, when they attained their adult phenotype. This change was dependent on the presence of neurons. In culture, most of these channel types were not expressed, but a phenotype more typical of that in vivo could be induced by co-culture with neurons. The electrophysiological properties of astrocytes make some existing hypotheses of astrocyte function less likely. 相似文献
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Analysis of Dysgenesis-Induced Lethal Mutations on the X Chromosome of a Q Strain of DROSOPHILA MELANOGASTER 总被引:4,自引:1,他引:3 下载免费PDF全文
The Q strain known as v6 was tested for its ability to induce X-linked lethal mutations in male and female hybrids from crosses with M strains in the P-M system of hybrid dysgenesis. All measurements of the mutation rate were made on the X chromosome derived from the v6 strain. The lethal rate for young hybrid males from the cross M female X v6 male was 1.11% per chromosome. For older males, it was only 0.44%, suggesting that there is less mutational or more repair activity in the germ cells of the older males or that mutant cells are selectively eliminated as the hybrid males age. The lethal rate for hybrid females from comparable crosses was approximately the same for both ages that were tested. However, it was substantially less than the rate for the hybrid males--only 0.26% per chromosome. Genetically identical hybrid females from reciprocal crosses also showed a low mutation rate, 0.13% per chromosome. Again, there was no difference between young and old flies. Mapping experiments established that most of the lethal mutations that were recovered from the male and female hybrids were located in two regions on the X chromosome, one between bands 14B13 and 15A9 , the other between bands 19A1 and 20A , which encompasses the maroonlike locus. More refined mapping of the lethals in the maroonlike region demonstrated that the vast majority of these affected a single gene located in band 19C4 . Cytological analysis of the lethal chromosomes revealed that several carried rearrangements, including inversions, duplications and deficiencies. Chromosome breakage occurred primarily in bands 14D1 -3 and 18F- 20A , and most of the breaks in the latter segment were located in 19C . However, rearrangements involving 19C and mutations of the gene in 19C4 were mutually exclusive events. In situ hybridization of a P element probe to the chromosomes of v6 demonstrated that P elements reside at a minimum of five sites on the X chromosome. These P element sites correspond to the mutational and breakage hot spots on that chromosome. The combined genetic and cytological data imply that most of the X-linked lethal mutations that occur in M X v6 hybrids are due to local P element action. Consideration of these and other data suggest that v6 is a weak P strain in the P-M system of hybrid dysgenesis and that other Q strains might also be regarded in this way. 相似文献
9.
Abstract— The levels of tritiated catecholamines and metabolites were measured in regions of the rat brain at intervals after the intraventricular injection of [3 H]dopamine, [3 H]nor-adrenaline and [3 H]normetanephrine. The disappearance of catecholamines and appearance of metabolites with time and the regional turnover rates of these amines indicate that the major pathway of the metabolism of noradrenaline and dopamine actively released from physiological storage sites is to the neutral alcoholic metabolites. The acid metabolites, homovanillic acid and 3,4-dihydroxyphenylacetic acid appear to be only minor products of normal dopamine metabolism in rat brain regions including the striate, but are the main end products of the metabolism of excess exogenous dopamine.
The active metabolism of stored noradrenaline to alcohol metabolites is also indicated by the increase in neutral alcohol metabolites accompanying the increased noradrenaline turnover when rats were subjected to electroshock stress. Therefore in the rat brain, neutral alcohol metabolites of dopamine and noradrenaline have great significance in the study of physiological catecholamine turnover in any region. 相似文献
The active metabolism of stored noradrenaline to alcohol metabolites is also indicated by the increase in neutral alcohol metabolites accompanying the increased noradrenaline turnover when rats were subjected to electroshock stress. Therefore in the rat brain, neutral alcohol metabolites of dopamine and noradrenaline have great significance in the study of physiological catecholamine turnover in any region. 相似文献
10.
A soluble 2,3-oxidosqualene sterol cyclase 总被引:5,自引:0,他引:5
P D Dean P R Ortiz de Montellano K Bloch E J Corey 《The Journal of biological chemistry》1967,242(12):3014-3015