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991.
The Crabtree effect (inhibition of respiration by glycolysis) is observed in cells with approximately equal glycolytic and respiratory capacities for ATP synthesis. Addition of glucose to aerobic suspensions of glucose-starved cells (Sarcoma 180 ascites tumor cells) causes a burst of respiration and lactate production due to ATP utilization for glucose phosphorylation by hexokinase and phosphofructokinase. This burst of activity is followed by inhibition of both respiration and glycolysis, the former to below the value before glucose addition (Crabtree effect). Both the respiratory rate and the glycolytic flux appear to be regulated by the cytosolic albeit by completely different mechanisms. Respiration is regulated by the free energy of hydrolysis of ATP, such that the rate increases as the decreases and decreases as the increases. The regulatory enzymes of glycolysis are activated by ADP (AMP) and Pi and inhibited by ATP. Thus both respiration and glycolysis increase or decrease as the decreases or increases. The parallel regulation of both ATP-producing pathways by this common metabolite ratio is consistent with the cytoplasmic being an important determinant of homeostatic regulation of cellular energy metabolism. 相似文献
992.
Khalil Ahmed Alan T. Davis Said A. Goueli Michael J. Wilson 《Biochemical and biophysical research communications》1980,96(1):326-332
32P-labelled chromatin proteins from rat liver and ventral prostate were fractionated according to the procedure designed to enrich high-mobility-group (HMG) nonhistone proteins. This fraction, however, reproducibly demonstrated small amounts of apparently basic nonhistone proteins other than HMG nonhistone proteins. These proteins appeared to be tissue specific and were highly labelled with 32P. The 32P-labelled phosphoproteins were soluble in trichloroacetic or perchloric acid, migrated in acid-urea polyacrylamide gels, and demonstrated pI values ranging from 6.8 to 7.5. The HMG proteins 1 and 2 showed no incorporation of radioactivity under these experimental conditions. 相似文献
993.
B. Labedan K.B. Heller A.A. Jasaitis T.H. Wilson E.B. Goldberg 《Biochemical and biophysical research communications》1980,93(2):625-630
DNA penetration from T4 phage adsorbed to was measured at different membrane potentials. There was a precipitous reduction in DNA penetration between 110 mV and 60 mV. This threshold of membrane potential for DNA penetration is independent of ΔpH and rather insensitive to external pH between 6 and 8. 相似文献
994.
995.
K L Molnar-Kimber S R Webb J Sprent D B Wilson 《Journal of immunology (Baltimore, Md. : 1950)》1980,125(6):2643-2645
To examine the relationship of T cell specificity for Mls vs H-2 determinants, BALB/c (H-2d,Mlsb)(d,b) T cells were stimulated repeatedly in vitro with H-2-compatible, Mls-incompatible DBA/2(d,a) stimulators. This line of T cells gave strong mixed-lymphocyte reactions to the priming Mlsa determinants but, in addition, gave appreciable responses to various foreign H-2 determinants. When this T cell line was subsequently stimulated over a period of 2 mo with Mlsa-negative cells of a particular foreign H-2 haplotype, e.g., H-2k, the cells gave high responses to H-2k determinants but only very low responses to third-party H-2 determinants. Significantly, the cells retained high reactivity for Mlsa determinants. In other experiments, BALB/c T cells positively selected to Mlsa,d-negative H-2-incompatible stimulator cells retained high reactivity for Mlsa determinants. The implications of these findings are discussed. 相似文献
996.
Rearrangement of immunoglobulin genes 总被引:21,自引:0,他引:21
997.
Counterion-induced condesation of deoxyribonucleic acid. a light-scattering study. 总被引:14,自引:0,他引:14
The addition of the trivalent or tetravalent cations spermidine or spermine to a solution of T7 DNA in aqueous solution causes an alteration of the DNA from its extended coil form to a condensed form. If performed at low DNA concentration and at low ionic strengths, this transformation results in a monomolecular collapse to form a particle with a hydrodynamic radius of about 500 A. We have monitored this change using quasielastic and total intensity light scattering. In a solution of 50% methanol in water, the divalent cations Mg2+ and putrescine also can cause the condensation of DNA. Using Manning's (1978) counterion condensation theory, we calculate a striking unity among these disparate ions: the collapse occurs in each case when from 89 to 90% of the DNA phosphate charges are neutralized by condensed counterions. 相似文献
998.
The transport of the bile salt, glycodeoxycholate, was studied in vesicles derived from rat jejunal and ileal brush border membranes using a rapid filtration technique. The uptake was osmotically sensitive, linearly related to membrane protein and resembled D-glucose transport. In ileal, but not jejunal, vesicles glycodeoxycholate uptake showed a transient vesicle/medium ratio greater than 1 in the presence of an initial sodium gradient. The differences between glycodeoxycholate uptake in the presence and absence of a Na+ gradient yielded a saturable transport component. Kinetic analysis revealed a Km value similar to that described previously in everted whole intestinal segments and epithelial cells isolated from the ileum. These findings support the existence of a transport system in the brush border membrane that: (1) reflects kinetics and characteristics of bile salt transport in intact intestinal preparations, and (2) catalyzes the co-transport of Na+ and bile salt across the ileal membrane in a manner analogous to D-glucose transport. 相似文献
999.
R C Steer M J Wilson K Ahmed 《Biochemical and biophysical research communications》1979,89(4):1082-1087
Nuclear membranes from rat liver contain a phosphoprotein phosphatase activity capable of dephosphorylating endogenous nuclear membrane phosphoproteins. This activity was also expressed towards the 32P-labeled exogenous phosphoprotein substrates phosvitin and lysine-rich histone. Differential effects of altered ionic strength, EDTA, pyrophosphate, and 2-mercaptoethanol on the phosphatase activity towards the two exogenous substrates suggest the presence of multiple phosphatases in the nuclear membrane. ATP, ADP, and sodium fluoride inhibited activity towards both exogenous substrates, while cyclic AMP or cyclic GMP at 10?6M had no apparent effect. 相似文献
1000.
The EPR absorption properties of the hemes of cytochrome oxidase and their liganded derivatives were examined in oriented multilayers from isolated oxidase, mitochondrial membranes and membrane fragments of a bacterium, Paracoccus denitrificans. The hemes of the oxidase in all the systems investigated were oriented normal to the plane of the multilayers. The directions of the g signals corresponding to the gx and gy axes of the g tensor were found to be different in low-spin ferric heme in fully oxidized oxidase and in half-reduced liganded oxidase. It is suggested that this different orientation of gx and gy in fully oxidized oxidase and half-reduced liganded oxidase arises because the respective EPR signals belong to two different hemes, those of cytochrome a and a3. 相似文献