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31.
Kinetic characterization of early intermediates in the folding of E. coli tryptophan-synthase beta 2 subunit 总被引:1,自引:0,他引:1
This report describes the use of fluorescence energy transfer between an intrinsic energy donor (tryptophan 177) and two chemically added acceptors to study intermediates in the folding of the beta 2 subunit of E. coli tryptophan-synthase. Two early folding steps are thus identified and characterized. One is very rapid (its rate constant at 12 degrees C is 0.02 sec-1) and corresponds to the folding of the N-terminal domain into a structure whose overall features approximate well those of the native domain. The second step is somewhat slower (its rate constant at 12 degrees C is 0.008 sec-1) and involves a conformational rearrangement of the N-terminal domain brought about by the interactions between the N- and C-terminal domains within a monomeric beta chain. This brings to five the number of intermediates which have been identified and ordered on the folding pathway of the dimeric beta 2 subunit. 相似文献
32.
Comparison of the effects of 1,2-dimethylhydrazine and cyclophosphamide on micronucleus incidence in bone marrow and colon 总被引:2,自引:0,他引:2
An in vivo micronucleus assay has been developed that utilizes colonic epithelial cells. The genotoxic effects of 1,2-dimethylhydrazine (54-07-3), a colon carcinogen, and of the nitrogen mustard, cyclophosphamide (50-18-0), on the bone-marrow polychromatic erythrocytes and on colonic epithelium from mice were compared using micronucleus induction in each organ as the end point. In the bone marrow, cyclophosphamide was a potent inducer of micronuclei, while 1,2-dimethylhydrazine administration had little effect on the micronucleus incidence. In the colon, 1,2-diemthylhydrazine was an effective inducer of micronuclei. Thus, the colonic micronucleus assay appears to be a potentially useful test for the detection of colon carcinogens. 相似文献
33.
Correct developmental expression of a cloned alcohol dehydrogenase gene transduced into the Drosophila germ line 总被引:59,自引:0,他引:59
We have used P-element-mediated transformation to introduce a cloned Drosophila alcohol dehydrogenase (Adh) gene into the germ line of ADH null flies. Six independent transformants expressing ADH were identified by their acquired resistance to ethanol. Each transformant carries a single copy of the cloned Adh gene in a different chromosomal location. Four of the six transformant lines exhibit normal Adh expression by the following criteria: quantitative levels of ADH enzyme activity in larvae and adults; qualitative tissue specificity; the size of stable Adh mRNA; and the characteristic developmental switch in utilization of two different Adh promoters. The remaining two transformants express ADH enzyme activity with the correct tissue specificity, but at a lower level than wild type. These results demonstrate that an 11.8 kb chromosomal fragment containing the Adh gene includes the cis-acting sequences necessary for its correct developmental expression, and that a variety of chromosomal sites permit proper Adh gene function. 相似文献
34.
Otto D. Hensens Ray S. Dewey Jerrold M. Liesch Mary A. Napier Robert A. Reamer Jack L. Smith Georg Albers-Schönberg Irving H. Goldberg 《Biochemical and biophysical research communications》1983,113(2):538-547
Spectroscopic evidence suggests the presence of a highly strained ether ring (Fig. 1) (possibly an epoxide) in the C12-subunit of the previously determined partial structure (Fig. 2) of the major neocarzinostatin chromophore (NCS-Chrom ) which completes assignment of all the oxygens in the molecule. The main product from mercaptan treatment suggests opening of the ether ring involving the addition of one molecule of mercaptan as well as reduction of the C12-substructure, whereas a parallel two-step reduction occurs on NaBH4 treatment. Both reactions occur with rearrangement of the C12-substructure and the implication for the mechanism of action of NCS-Chrom in DNA strand scission activity is discussed. The evidence suggests a downward revision of the molecular formula for NCS-Chrom as well as minor components and by two protons. 相似文献
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Abstract— Microsomes and synaptosomes from rat brain accumulated 4,5Ca against a concentration gradient by an ATP-dependent process. Calcium accumulation occurred to the same extent in microsomes prepared from white matter and from grey matter, an observation suggesting that calcium uptake may be in part an activity of the axonal membrane. Microsomes and synaptosomes accumulated calcium to a similar extent but less actively than mitochondria. By contrast, synaptic vesicles showed relatively little calcium accumulation. Isotonic concentrations of sucrose, NaCl, KCl and choline chloride inhibited calcium accumulation, with NaCl and KCl the least effective of these inhibitory agents. No consistent effects on calcium uptake were obtained with adenosine 3′,5′-monophosphate, dibutyryl cyclic AMP or the methyl xanthines. Incubation of prelabelled microsomes resulted in a release of 45Ca, and ATP inhibited this release process. In the absence of added ATP, isotonic NaCl promoted calcium release to a significantly greater extent than KCl choline chloride or sucrose. In the presence of ATP, these agents all promoted a similar degree of release. Adenosine 3′,5′-monophosphate or agents that affect its metabolism did not significantly affect calcium release. Magnesium ions reduced calcium release under all conditions tested. 相似文献
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Hyperthyroidism may be associated with hypokalemic periodic paralysis. Two cases are presented demonstrating intermittent attacks of flaccid paralysis associated with clinical symptoms, signs and laboratory findings of hyperthyroidism. During an attack, one patient had a serum potassium of 2.1 mEq. per litre.Various factors such as trauma, exposure to cold, excessive carbohydrate ingestion and certain medications have been stated to precipitate an episode of paralysis. Attacks may range from mild weakness to generalized flaccid paralysis with loss of deep tendon reflexes. Several reported patients have died owing to cardiac arrest or respiratory paralysis.During attacks, the serum potassium is usually in the range of 2.2 to 3.2 mEq. per litre. It is postulated that a metabolic abnormality affecting the muscle-cell membrane can occur in the hyperthyroid state resulting in a shift of potassium to the intracellular position, thus producing a situation of hyperpolarization of the muscle-cell membrane which in turn alters the muscle contractibility.The importance of recognizing the unusual association of hypokalemic periodic paralysis with hyperthyroidism is stressed because, with successful treatment of the hyperthyroidism, the episodes of paralysis disappear. 相似文献
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