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101.
A stochastic theory of cell kinetics has been developed based on a realistic model of cell proliferation. A characteristic transit time, i, has been assigned to each of the four states (G1, S, G2, M) of the cell cycle. The actual transit time, ti, for any cell is represented by a distribution around i with a variance σi2. Analytic and computer formulations have been used to describe the time development of such characteristics as age distribution, labeling experiments, and response to perturbations of the system by, for example, irradiation and temperature. The decay of synchrony is analyzed in detail and is shown to proceed as a damped wave. From the first few peaks of the synchrony decay one can obtain the distribution function for the cell cycle time. The later peaks decay exponentially with a characteristic decay constant, λ, which depends only on the average cell-cycle time, , and the associated variance. It is shown that the system, upon any sudden disturbance, approaches new “equilibrium” proliferation characteristics via damped periodic transients, the damping being characterized by λ. Thus, the response time of the system, /λ, is as basic a parameter of the system as the cell-cycle time. 相似文献
102.
Spectral Studies of Iron Coordination in Hemeprotein Complexes: Difference Spectroscopy below 250 mμ 下载免费PDF全文
In order to evaluate the feasibility of observing the spectral behavior of protein groups in the coordination sphere of the iron in hemeproteins, criteria are developed to determine whether or not the application of difference absorption spectroscopy to the study of complex formation will be successful. Absolute absorption spectra, 300-1100 mmu, from bacterial catalase complexes are displayed, and the infrared bands correlated with magnetic susceptibility values of similar complexes of other hemeproteins. Dissociation constants for the formation of cyanide and azide complexes of metmyoglobin, methemoglobin, bacterial catalase, and horseradish peroxidase are given. Difference spectra, 210-280 mmu, are displayed for cyanide and azide complexes of these hemeproteins. A band at 235-241 mmu is found in the difference spectra of all low-spin vs. high-spin complexes. The factors which favor the assignment of this band to a transition involving a histidine residue are presented. 相似文献
103.
The Effect of 2,3,6-Trichlorophenylacetic and 2,2-Dichloropropionic Acids on Nitrite Oxidation 下载免费PDF全文
The effects of two herbicides, 2,3,6-trichlorophenylacetic acid, sodium salt, and 2,2-dichloropropionic acid, sodium salt, on nitrite-oxidizing bacteria were studied by the soil perfusion technique. The time of application of 2,3,6-trichlorophenylacetic acid affected its toxicity to the nitrifier. When it was present in the environment as the nitrifier started growth, it was more toxic than if the organisms were allowed to nitrify actively before they were subjected to the herbicide.
The herbicide 2,2-dichloropropionic acid at rates up to 700 ppm had little effect on nitrite oxidation. The toxicity of 2,3,6-trichlorophenylacetic acid for Nitrobacter was reduced by 2,2-dichloropropionic acid irrespective of whether the cells came into contact with the agents before or during active oxidation. The mode of action for this phenomenon has not been determined.
相似文献104.
105.
Stanley G. Schultz Ralph Zalusky Arthur E. Gass Jr. 《The Journal of general physiology》1964,48(2):375-378
Unidirectional Cl fluxes across in vitro segments of rabbit ileum have been determined both in the absence and in the presence of an electrochemical potential gradient. The results indicate that Cl transport in this preparation can be attributed to purely passive forces uninfluenced by solvent drag or exchange diffusion. Furthermore, on the basis of this and previous studies, it has been demonstrated that the sum of the partial ionic conductances of Na and Cl accounts for at least 90 per cent of the total tissue conductance. 相似文献
106.
Arthur Leznoff Harold Frank Paul Telner Jacob Rosensweig J. Leonard Brandt 《CMAJ》1964,91(22):1154-1160
Although Montreal is in an endemic area, significant clinical histoplasmosis with systemic manifestations has been, until recently, infrequently diagnosed. However, since the autumn of 1963, 31 cases of clinically significant histoplasmosis have been seen by the authors. These were divided into two groups: (1) patients in whom the diagnosis was established on the basis of histological and/or cultural demonstration of the fungus; (2) patients in whom the diagnosis was based on a positive histoplasmin skin test, a complement fixation antibody titre of 1:32 or greater and compatible clinical and radiological findings. An additional group of 11 patients who presented with erythema multiforme was investigated and a heretofore unrecognized relationship between histoplasmosis and erythema multiforme was established. 相似文献
107.
108.
We have examined the nature of the circular dichroism band at 330 mμ for a series of copolymers of β-p-nitrobenzyl L -aspartate with β-benzyl L -aspartate. The circular dichroism band arises from an electronic transition in the nitroaromatic group. In order to interpret the effect quantitatively, we employed a simplified statistical treatment and curve fitting for six copolymers. Both approaches gave consistent results, which indicates that the dichroism comes from pairwise interactions between two nitrobenzyl groups. We constructed a molecular model that meets the constraints and requirements of the analyses developed in this paper. In this model, it is proposed that the main chain forms a right-handed α-helix and that nitrobenzyl groups separated by four residues interact with each other. 相似文献
109.
The left internal mammary artery implant combined with epicardiectomy and free omental graft provides three extra-coronary sources of blood. This operation tested in dogs with 92% main-stem occlusion of three coronary arteries protected 75% of the animals. Applied clinically in over 100 patients, the operation resulted in 90% improvement. To obtain complete myocardial revascularization, the right internal mammary artery has been used as a fourth source of extra-coronary blood. In 57 animals, the right internal mammary arteries were implanted into the anterior walls of the right ventricle; in 80% this vessel formed anastomoses with the right coronary tree, and in 65% with the right and left coronary arteriolar systems. Six patients are described who underwent right internal mammary artery implantation; five of these in addition had the combined operation of left internal mammary artery implant, epicardiectomy and free omental graft. All patients had completely blocked right coronary arteries; in addition, five had advanced disease of the left coronary arterial tree. 相似文献
110.