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181.
The oxidative and phosphorylative properties of mitochondria isolated from Neurospora crassa were investigated as a function of growth stage. The rates of oxidation of exogenous NADH and NADPH varied independently of each other, thus ruling out the existence of only one unspecific dehydrogenase. Two different pathways were involved in the oxidation of NAD-linked substrates, as indicated by changes in the rate of oxygen uptake, the sensitivity to rotenone, and the efficiency of phosphorylation. One pathway was sensitive to rotenone and involved three energy-coupling sites, whereas the other was resistant to rotenone and bypassed complex I. Our results indicated that the activity of complex I of the respiratory chain increased markedly in the late exponential phase of growth, remained high in the stationary phase, and then decreased when conidiae were formed. In contrast, the activity of the rotenone-resistant bypass was maximal in the early exponential phase. With malate (plus glutamate) as a substrate, the sensitivity to rotenone and the ADP/O ratios were always lower than those observed with other NAD-linked substrates, suggesting a possible cooperation between malate dehydrogenase and the rotenone-resistant pathway. The rate of oxygen uptake measured in the presence of rotenone was significantly increased by the addition of exogenous NAD+, suggesting that added NAD+ could interact with the rotenone-resistant bypass. 相似文献
182.
Gerald R. Palmer David C. Clark Peter M. Bayley David B. Sattelle 《Journal of molecular biology》1982,160(4):641-658
Quasi-elastic light scattering has been used to characterize the oligomeric properties of solutions of glycerol-cycled bovine microtubule protein, and the properties of the 30 S oligomeric species and 6 S tubulin heterodimer prepared by gel filtration on Sepharose 6B. It is shown that in dimer preparations, as little as 0.04% by number of 30 S rings would account for the difference between an observed mean diffusion coefficient D20, W = 3.1 × 10?7 cm2 s?1 and the value of D20, W = 5.1 × 10?7 cm2 s?1 calculated for tubulin dimer of Mrel 100,000. The 30 S ring has an observed diffusion coefficient of D20, W = 0.49 × 10?7 cm2 s?1. These values are not changed significantly by the presence of 4 m-glycerol, indicating the persistence of 6 S and 30 S forms for dimer and ring, respectively.Mixtures of ring and dimer components of this preparation behave as a non-interacting two-component system, indicating the absence of substantial re-equilibration between the species at 5 °C and pH 6.5.The effect of salt on ring and microtubule protein samples indicates partial dissociation, consistent with the formation of additional intermediate oligomeric forms.In quasi-elastic light scattering measurements adapted to kinetic studies, changes in the oligomeric composition of microtubule protein are detected in the early stages of the reversible assembly process at pH 6.5. A 25% decrease in scattered light intensity, without significant change in mean diffusion coefficient, indicates the lability of the ring oligomeric structures, which undergo partial transformation to alternative oligomeric species under these assembly conditions. 相似文献
183.
Cotton ovules cultured in an insufficiency of boron (10 micromolar), showed inhibition of fiber growth by the ninth day in culture. Averaging data from eight to eleven days of culture under these conditions, total incorporation of [6-14C]orotic acid into fiber was inhibited by 59%. Inhibition was evident in all radioactively labeled pools, indicating that the effect may be at the membrane transport level or at an early stage of orotic acid metabolism. On a per cent basis, incorporation into RNA under boron deficiency was higher than under sufficiency. The effect is greater on the eighth day of culture, with a decreasing difference from controls up to the eleventh day. Conversely, the per cent incorporation into UDP-glucose was lower under boron deficiency than in controls, having a more or less constant value from 8 to 11 days of culture. Thus, a primary event of boron deficiency in cotton fiber culture is an alteration in the flow of metabolites through the pyrimidine synthesis pathway. 相似文献
184.
In a trial of postoperative adjuvant chemotherapy women with primary breast cancer and spread to one or more axillary nodes were randomised to receive a six-month course of either the single agent chlorambucil or the five-drug combination of chlorambucil, methotrexate, fluorouracil, vincristine, and adriamycin. On completing the treatment 47 patients were asked to fill in questionnaires at home on the side effects of treatment and its influence on the quality of their life. Side effects including nausea, vomiting, malaise, and alopecia had been severe enough to interfere with their lifestyle in 9 (42%) of the patients who had received the single agent and 19 (79%) of those who had received multiple-drug treatment. Various other side effects were reported by a few patients. Seven (29%) of the patients who had received the multiple-drug schedule voluntarily added that the treatment had been "unbearable" or "could never be gone though again." The proportion of patients who had experienced severe side effects while receiving the treatment was considerable; hence such adjuvant chemotherapy is justifiable only if it will substantially improve a patient''s prognosis. 相似文献
185.
Resonance Raman studies of oxidized and reduced cytochrome oxidase and liganded derivatives of the oxidized enzyme have been performed by using direct-Soret excitation at 413.1 and 406.7 nm, as well as near-Soret excitation (457.9 nm) and alpha-band excitation (604.6 nm). The Soret results clearly show selective enhancement of Raman modes of the hemes of cytochromes a and a3, depending upon the excitation wavelength chosen. For the preparations employed in this study, photoreduction of cytochrome oxidase in the laser beam was not a significant problem. Resonance Raman frequencies sensitive to oxidation state and spin state or core expansion of the a and a3 hemes are identified and correlated with those previously identified for other heme proteins. An unusual low-frequency (less than 500 cm(-1)) spectrum is observed for oxidized high-spin cytochrome a3, which may be due to axial nonheme structures in this cytochrome. 相似文献
186.
SDS electrophoresis gels of complex III from yeast mitochondria were run after incubation of the enzyme at several different temperatures. It was found that the intensity of the more slowly moving core protein band was substantially affected by the incubation temperature. Four low molecular weight polypeptides were eluted from gels electrophoresed after preincubation of the enzyme at 15° C for 12 hours. These polypeptides were then incubated for 5 minutes at 100° followed by SDS gel electrophoresis. A polypeptide with the same molecular weight as the anomalous core protein was resolved. 相似文献
187.
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189.
The photochemical reaction centers from a variety of purple photosynthetic bacteria are composed of a trimer of protein subunits. However, the recently isolated reaction center from Rhodopseudomonas gelatinosa appears to have only two subunits. In this paper we examine the EPR characteristics of the primary photochemical reactants in this species, and compare them with those of other species. Despite of the differences in protein composition, no dramatic differences in EPR properties are seen in vivo, although some interesting effects are seen upon solubilization of the reaction center, which may be related to the unusual lability of the isolated preparation. Perhaps the most noteworthy phenomenon seen in Rps. gelatinosa is the apparent ability of electrons on the reduced intermediary electron carrier to tunnel at low temperatures to the oxidized c-type cytochrome, which has not been seen in other species studied to date. 相似文献
190.