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91.
In order to regulate cell volume during hyperosmotic stress, the intertidal copepod Tigriopus californicus, like other aquatic crustaceans, rapidly accumulates high levels of intracellular alanine, proline, and glycine. Glutamate-pyruvate transaminase (GPT; EC 2.6.1.2), which catalyzes the final step of alanine synthesis, is genetically polymorphic in T. californicus populations at Santa Cruz, California. Spectrophotometric studies of homogenates derived from a homozygous isofemale line of each of the two common GPT alleles indicated that the GPTF allozyme has a significantly higher specific activity than the GPTS allozyme. Under conditions of hyperosmotic stress, individual adult copepods of GPTF and GPTF/S genotypes accumulated alanine, but not glycine or proline, more rapidly than GPTS homozygotes. When young larvae were subjected to the same hyperosmotic conditions, GPTS larvae suffered a significantly higher mortality than GPTF or GPTF/S larvae. These results suggest that the biochemical differences among GPT allozymes result in specific physiological variation among GPT genotypes and that this physiological variation is manifested in differential genotypic survivorships under some naturally occurring environmental conditions.This work was supported in part by a grant from the Lerner Fund for Marine Research of the American Museum of Natural History, an NIH Training Grant in Integrative Biology, and NIH Grants GM 28016 and GM 10452. 相似文献
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94.
The systemic anaphylactic reaction and thein vitro anaphylactic contraction of the terminal segment of the ileum performed according to the Schultz-Dale technique, were elicited in guinea pigs passively sensitized with rabbit antibodies to human serum albumin, using whole and cathepsin D degraded antigen. The intensity of the systemic anaphylactic response that was evoked by degraded antigen was lower; a highly significant suppression of the response was obtained provided an antigen degraded more than by 70% was injected. With an increasing degradation of antigen, more animals responded with lower or even with no reaction; the number of animals developing severe or lethal shock, decreased at the same time. The number of animals that developed a medium anaphylactic response remained at the same level. The degraded antigen did not evoke the anaphylactic contraction of the terminal segment of the ileumin vitro, and moreover, it blocked the contraction after addition of the whole antigen. 相似文献
95.
96.
H. Steffen M. Da Prada A. Pletscher 《Biochimica et Biophysica Acta (BBA)/General Subjects》1974,338(2):561-571
THe quantum yield, the life time and the degree of polarization of the fluorescence of intact chromaffin granules isolated from bovine adrenal medulla were compared to those of catecholamines solutions and catecholamine/ATP mixtures. Rising concentrations of catecholamines in aqueous solutions exhibited increasing quenching and decreasing life times indicating that the quenching was collision induced. Similar effects occurred in mixtures of catecholamines with ATP and Ca2+ showing that the nucleotide did not remarkedly hinder the mobility of the catechol group. In suspensions of whole granules stron quenching and shortening of life time was observed compared with solutions of disrupted granules. Fluorescence yield and life time were decreased by about the same factor suggesting that storage of the amines was not correlated with a major immobilization of the catechol group. The degree of polarization of intact granules was higher than that of solutions of catecholamines alone, but similar to catecholamine/ATP mixtures with concentrations corresponding to those found in the granules. This indicates an interaction of catecholamines with ATP in the granules. The results are in agreement with a storage model for catecholamines in the chromaffin granules of adrenal medulla in which catecholamines are bound to ATP, but in a non-rigid way. 相似文献
97.
The glutamate permeation system in Escherichia coli K-12 consists of three genes: gltC, gltS, and gltR. The genes gltC and gltS are very closely linked, and are located between the pyrE and tna loci, in the following order: tna, gltC, gltS, pyrE; gltR is located near the metA gene. The three glt genes constitute a regulatory system in which gltR is the regulator gene responsible for the formation of repressor, gltS is the structural gene of the glutamate permease, and gltC is most probably the operator locus. The synthesis of glutamate permease is partially repressed in wild-type K-12 strains, resulting in the inability of these strains to utilize glutamate as the sole source of carbon. Derepression due to mutation at the gltC locus enables growth on glutamate as a carbon source both at 30 C and at 42 C. Temperature-sensitive gltR mutants capable of utilizing glutamate for growth at 42 C but not at 30 C were found to be derepressed for glutamate permease when grown at 42 C and partially repressed (wild-type phenotype) upon growth at 30 C. These mutants produce an altered thermolabile repressor which can be inactivated by mild heat treatment (10 min at 44 C) in the absence of growth. 相似文献
98.
Genetic and Physiological Analysis of Glutamate Decarboxylase in Escherichia coli K-12 总被引:3,自引:1,他引:2
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No correlation was found between glutamate decarboxylase (GAD) activity and the ability of Escherichia coli K-12 strains to grow on glutamate. A gene, gad, determining GAD activity maps near gltC, which controls glutamate permease. 相似文献
99.
L Marcus H Ris H O Halvorson R K Bretthauer R M Bock 《The Journal of cell biology》1967,34(2):505-512
This report details the procedural requirements for preparing cell-free extracts of yeast rich in polyribosomes. This enabled us to demonstrate the occurrence of polyribosomes in yeast, to show their role in protein synthesis, and to devise methods for their resolution and isolation. When certain precautions are met (the use of log phase cells, rapidly halting cell growth, gentle methods of disruption, sedimentation through exponential density gradients, etc.), individual polyribosome size classes ranging up to the heptosome can be fractionated and separated from their nearest neighbors. Larger size classes are resolved partially among themselves, free of smaller polyribosomes. This was confirmed by extensive electron micrographic studies of material from the various fractions obtained upon density gradient centrifugation of yeast extracts. Modifications of the gradients and procedure should allow fractionation and isolation of the larger polyribosomes, including those containing polycistronic messages. Yeast polyribosomes are disaggregated to single ribosomes by longer term grinding, cell disruption by the French pressure cell, the Hughes press, or by incubation with dilute RNAse. Yeast polyribosomes are active in the incorporation of amino acids into polypeptide; the single ribosomes exhibit only slight activity. The latter activity is probably due to the presence of a small fraction of monosomes still containing mRNA. Poly-U stimulates amino acid incorporation only in the single ribosomes. 相似文献
100.
Genetic Analysis of Glutamate Transport and Glutamate Decarboxylase in Escherichia coli 总被引:13,自引:10,他引:3
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The location of the Escherichia coli K-12 genes determining or regulating glutamate transport, and the location of the gene determining glutamate decarboxylase synthesis, were established by conjugation. The ability to grow on glutamate as the sole source of carbon and energy was used to select for glutamate transport recombinants. Two genes determining the ability to grow on glutamate as the sole source of carbon and energy were mapped. One (gltC) is located near mtl (mannitol), and the other (gltH) appears to be located between the gal (galactose) and trp (tryptophan) loci. The glutamate decarboxylase gene (gad) is strongly linked to gltC. The gltC(+) recombinants grow on glutamate much faster and accumulate this amino acid to a greater extent than do the gltH(+) recombinants. The gltH(+) gene functioned only in one female strain (P678), whereas the gltC gene functioned in all the female strains tested (P678, C600, W1). 相似文献