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111.
Charles A. Owen 《Biological trace element research》1981,3(3):217-224
The subcutaneous injection of Walker 256 carcinosarcoma cells into a rat was followed by a pronounced increase in plasma ceruloplasmin activity. This lasted only about 3 weeks even though the tumors were still enlarging rapidly. Based upon studies with67Cu, the increase in plasma ceruloplasmin seemed to reflect increased production of the enzyme by the livers of rats bearing the tumors. Injections of turpentine also raised plasma ceruloplasmin, but to a significantly lesser extent and normal values were reached within 2 weeks. 相似文献
112.
113.
A deterministic predator-prey model is presented for describing the dynamics of a solid tumor in the presence of a specifically
reactive lymphocyte population which is stimulated by, and antagonistic to, the tumor. The qualitative behavior of the solutions
is developed and briefly compared to the results of transplantation experiments. Although the model is primitive, it leads
to predictions that are in general agreement with observation and intuitive expectations. In particular, it is found that:
(1) very low levels of transplanted tumor will not survive in the recipient. (2) At somewhat higher levels, tumor growth will
be uncontrolled in the syngeneic recipient. However, immune intervention if early enough, can lead to control and elimination
of the tumor. (3) At still higher levels of transplanted tumor, no amount of immune intervention will be effective in controlling
the tumor. (4) If the recipients immune system is suppressed prior to transplantation, or is debilitated for any reason, the
chance that the tumor will grow increases. (5) If the recipients immune system is stimulated prior to transplantation, the
chance of tumor survival decreases. (6) The survival of the tumor is much more sensitive to changes in tumor parameters (for
example, antigenicity) than in lymphocyte parameters. In addition it makes the unintuitive prediction that (7) There areisolated instances under which anincrease in the number of lymphocytes canincrease the chance of tumor survival. 相似文献
114.
Charles J. Mode 《Bulletin of mathematical biology》1977,39(6):693-704
Stochastic models of human reproduction are beginning to play significant roles in the evaluation of family planning programs.
A class of stochastic processes called absorbing, agedependent, semi-Markov processes frequently arises in the construction
of such models. The paper begins with a discussion of some technicalities regarding absorbing, age-dependent, semi-Markov
processes. Then, an algorithm due to Littman, which makes possible the computerization of this class of stochastic processes,
is presented. Briefly, Littman’s algorithm provides an efficient method for numerically solving systems of renewal type integral
equations, provided the system does not contain a large number of equations. After setting down a concrete model for a large
clinical trial of intrauterine devices conducted in Taiwan, the paper concludes with a discussion of a method for validating
the model based on the data collected in the clinical trial.
Presented at the Society for Mathematical Biology Meeting, University of Pennsylvania, Philadelphia, August 19–21, 1976. 相似文献
115.
Tritiated GA1 and four of its synthetic derivatives were studiedin relation to their biological activity, uptake and metabolismby barley aleurone layers. Incubation was done in the presenceand absence of ABA. Tentative identification of some of themetabolites was made by TLC and GLC radiocounting of the metaboliteand its acid hydrolyzed derivative. Only GA1 promoted -amylase synthesis. Uptake ranged from 20to 42%, varying with the derivative. ABA enhanced uptake of[3H]GA1 and [3H]pseudoGA1 and inhibited uptake of [3H]ketoGA1the Wagner-Meerwein rearrangement product of [3H]GA1 Uptakeof [3H]GA1 methyl ester ([3H]GA1-Me) and [3H]dihydroGA1 wasunaffected by ABA. [3H]GA1 was converted to an amphoteric GA1 derivative ([3H]amphoGA1)and [3H]GA1-glycosyl ester. GA1-Me was metabolized to four products,all of them GA1 derivatives, including an apparent amphotericGA1 derivative. DihydroGA1 was quite stable; only one metabolitewas produced in sufficient yield to analyze. This product didnot cochromatograph with either of the expected acid hydrolyzedepimers of [3H]dihydroGA1. [3H]ketoGA1 was readily metabolizedto one product, probably the glycoside. [3H]pseudoGA1 remainedessentially unmetabolized. Metabolism of all compounds testedwas not dramatically affected by ABA. Surprisingly, no metabolitesfrom hydroxylation at the 2-position were found.
1 Present address: Monsanto Agricultural Co., 800 N. LindberghBlvd., St. Louis, MO 63166, U.S.A. (Received January 31, 1977; ) 相似文献
116.
Summary Mark-release-recapture experiments performed with natural populations of Drosophila at Mather, California show that flies tend to return to their area of original capture or an area ecologically similar to it. Such habitat choice explains the microgeographic genetic differentiation we observed in the population. This behavioral difference between the flies may have a genetic component or may be environmentally induced. Either way, the results help explain how high levels of genetic variation are maintained by natural selection in these species. 相似文献
117.
118.
Genetic distances (D's) between five species within each of the families Mimidae and Vireonidae were estimated from frequencies of protein electromorphs at 23 loci. For three mimid species in the genus Toxostoma,
equals 0.084 (range, 0.069–0.104); and among three mimid genera,
equals 0.223 (0.167–0.278). These distances typify values previously reported in other birds at comparable levels of taxonomic recognition. In sharp contrast, the mean genetic distance among five congeneric species of Vireonidae is far higher,
=0.360 (0.027–0.578). One possible explanation for these results is that Vireo species are considerably older, on the average, than are species of Toxostoma or than are members of several other avian genera assayed to date. Conventional thought about the origin and relative age of the Vireonidae appears compatible with this explanation. Although genetic distances in the Vireonidae are large by avian standards, they remain modest or even small in comparison with distances between many nonavian vertebrate congeners. Results for the Mimidae and the Vireonidae are directly contrasted with genetic distances in well-known genera of Amphibia and Reptilia.This research was supported by NSF Grant DEB 7814195 and by a grant from the American Philosophical Society. 相似文献
119.
P A Weinhold L Charles M E Rounsifer D A Feldman 《The Journal of biological chemistry》1991,266(10):6093-6100
We examined the effect of fatty acids on phosphatidylcholine synthesis and cytidylyltransferase activity in Hep G2 cells. Treatment of Hep G2 cells with oleic acid caused an increase in the incorporation of [methyl-14C]choline into phosphatidylcholine and a corresponding decrease in radioactivity in choline phosphate using a pulse-chase procedure. This result is consistent with a fatty acid-induced increase in the cytidylyl-transferase step in the choline pathway. We measured cytidylyltransferase activity in membrane fractions and in cytosol (100,000 x g supernatant or soluble enzyme released by digitonin). The activity increased in both membrane and cytosol. Thus, an increase in total activity occurred. Cytidylyltransferase protein determined by Western blot immunoassay increased after oleic acid treatment. Immunotitration of cytidylyltransferase protein also indicated that an increase in enzyme protein resulted from oleic acid treatment. Cycloheximide did not prevent the oleic acid-induced increase in cytidylyltransferase activity. The increase in enzyme activity was apparent when we measured the activity in the presence or absence of lipid activators. Separation of cytosolic cytidylyltransferase into H- and L-forms showed that the increase in cytosolic activity was due to an increase in H-form. The amount of L-form did not change. We interpret these results to suggest that fatty acid treatment of Hep G2 cells promoted the formation of active cytidylyltransferase (H-form) from a preexisting inactive form. The increased activity was distributed between membranes and the lipoprotein form in cytosol (H-form). 相似文献
120.
The plastid ribisomal RNA (rRNA) operon of the achlorophyllous root parasite Conopholis americana was completely sequenced. Full-length rRNA genes are retained in the gene cluster, but significant divergence has occurred in the 16S, 23S and 5S genes. Both the 16S–23S intergenic spacer and the 4.5S–5S intergenic spacer have suffered substantial deletions, including the two tRNA genes typically found in prokaryotic and plastid 16S–23S spacers. 相似文献