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11.
Adenosine monophosphate is required for the activation of glycogen phosphorylase b and for release of the inhibition of phosphorylase a by glucose. Two molecules of adenosine monophosphate (AMP) bind to symmetry related sites at the subunit interface of the phosphorylase dimer. Adenosine triphosphate (ATP) binds to the same site, but does not promote catalytic activity. The structure of glucose-inhibited phosphorylase a bound to AMP and also of the complex formed with glucose and ATP is described. Crystallographic refinement of these complexes reveals that structural changes are associated with AMP but not ATP binding. The origin of these effects can be traced to different effector binding modes exhibited by AMP and ATP, respectively. The conformational changes associated with AMP binding traverse multiple paths in the enzyme and link the effector and catalytic sites. 相似文献
12.
Structural basis for the activation of glycogen phosphorylase b by adenosine monophosphate 总被引:12,自引:0,他引:12
S R Sprang S G Withers E J Goldsmith R J Fletterick N B Madsen 《Science (New York, N.Y.)》1991,254(5036):1367-1371
13.
Microspectrophotometry of photoreceptor organelles from eyes of the prawn Palaemonetes 总被引:3,自引:0,他引:3
Microspectrophotometric measurements of individual dark-adapted rhabdoms of the prawn Palaemonetes vulgaris reveal the presence of two light-sensitive pigments. A pigment with maximum absorbancy at 555 nanometers is converted by light to a long-lived intermediate with wavelength of maximum absorbancy at 496 nanometers. A second pigment with wavelength of maximum absorbancy at 496 nanometers bleaches in the light, seemingly without forming detectable products at wavelengths longer than 375 nanometers. Both pigments occur in each layer of microvilli. 相似文献
14.
Lanceolate bifacial points, including one fluted specimen, have been collected from beneath an early Holocene tephra at the Uptar site, northeastern Siberia. Thus, the technology associated with the well-known Paleoindian tradition was not confined to the Americas. The Uptar collection does not compare readily with other Beringian complexes and demonstrates that there is greater diversity in the archaeological record of northeastern Siberia than traditional colonization models imply. 相似文献
15.
Domain separation in the activation of glycogen phosphorylase a 总被引:3,自引:0,他引:3
E J Goldsmith S R Sprang R Hamlin N H Xuong R J Fletterick 《Science (New York, N.Y.)》1989,245(4917):528-532
The crystal structure of glycogen phosphorylase a complexed with its substrates, orthophosphate and maltopentaose, has been determined and refined at a resolution of 2.8 angstroms. With oligosaccaride bound at the glycogen storage site, the phosphate ion binds at the catalytic site and causes the regulatory and catalytic domains to separate with the loss of stabilizing interactions between them. Homotropic cooperativity between the active sites of the allosteric dimer results from rearrangements in isologous contacts between symmetry-related helices in the subunit interface. The conformational changes in the core of the interface are correlated with those observed on covalent activation by phosphorylation at Ser14 (phosphorylase b----a). 相似文献
16.
Carbon monoxide and human health 总被引:10,自引:0,他引:10
17.
Respiratory exposure to lead: epidemiological and experimental dose-response relationships 总被引:2,自引:0,他引:2
Epidemiologic studies of blood lead levels in general and occupational groups show a logarithmic regression on estimated atmospheric exposure. Experimental results at the same and higher levels show a dose-response relationship which fits the same regression. The data imply that long-term increases in atmospheric lead will result in predictably higher blood lead levels in the exposed populations. 相似文献
18.
The 12 Virginia barrier islands are divided into three groups on the basis of historical retreat rates and characteristics. The growth and reversal of inlet offsets is a long-term event that results from the operation of known coastal processes. Both geomorphic evidence and wave refraction analyses indicate that shoreline irregularity will diminish with time. There is no basis for the prediction (or expectation) that cape-like features will evolve along this shoreline. 相似文献
19.
K H Hoblet M L Eastridge C S Hayhow P D Goldsmith J R Staubus 《Journal of the American Veterinary Medical Association》1991,198(6):1028-1034
An 87-cow dairy herd with a history of high milk production was visited because of reduced reproductive performance and decreasing milk production. Cows that had recently delivered calves were thin, and many cows had evidence of previous episodes of laminitis. A ration that provided an unfavorable forage-to-concentrate ratio was being fed. In addition to various diagnostic efforts, management changes that were made included alteration of the ration and installation of a computer-operated feeder. After the initial visit, the herd was monitored for 30 months by the use of Dairy Herd Improvement monthly herd summary data. Several potential strengths and weaknesses of using selective production and reproduction monthly summary statistics were illustrated by this study. Milk production, as monitored by mature-equivalent production and average relative value-milk, continued to increase throughout the 30 months after intervention. Reproductive performance, as indicated by first-service conception rate, did not begin to improve until the final 6 months of the monitoring period. Overall, in addition to assisting in diagnostic efforts. Dairy Herd Improvement monthly herd summary data may be used to establish goals, provide comparisons, and maintain producer interest after practitioner intervention in herd management. 相似文献
20.
An integrated broiler company experienced a major outbreak of pullorum disease during 1990. The outbreak resulted in the distribution of Salmonella pullorum-infected birds to more than 150 roaster flocks in five states. Twenty-two parent (multiplier) breeder flocks became infected. An epizootiological investigation uncovered a grandparent male line breeder flock as the index flock supplying males to the affected parent flocks. Transmission apparently occurred vertically through the egg and horizontally by contact in the hatcheries and by placement of chicks on contaminated litter. 相似文献