Allosteric effect of ATP on Na(+),K(+)-ATPase conformational kinetics

The kinetics of the E2 --> E1 conformational change of unphosphorylated Na+,K+-ATPase was investigated via the stopped-flow technique using the fluorescent label RH421 (pH 7.4, 24 degrees C). The enzyme was pre-equilibrated in a solution containing 25 mM histidine and 0.1 mM EDTA to stabilize the E2 conformation. When rabbit enzyme was mixed with 130 mM NaCl alone or with 130 mM NaCl and varying concentrations of Na2ATP simultaneously, a fluorescence decrease was observed. In the absence of ATP, the fluorescence decrease followed a biexponential time course, but at ATP concentrations after mixing of >or=50 microM, the fluorescence transient could be adequately fitted by a single exponential. On the basis of the agreement between theoretical simulations and experimental traces, we propose that in the absence of bound ATP the conformational transition occurs as a two step reversible process within a protein dimer, E2:E2 --> E2:E1 --> E1:E1. In the presence of 130 mM NaCl, the sum of the forward and backward rate constants for the E2:E2 --> E2:E1 and E2:E1 --> E1:E1 transitions were found to be 10.4 (+/-1.0) and 0.49 (+/-0.02) s-1, respectively. At saturating concentrations of ATP, however, the transition occurs in a single reversible step with the sum of its forward and backward rate constants equal to 35.2 (+/-0.3) s-1. It was found that ATP acting at a high affinity site (Kd approximately 0.25 microM), stimulated the reverse reaction, E1ATP --> E2ATP, in addition to its known allosteric low affinity (Kd approximately 71 microM) stimulation of the forward reaction, E2ATP --> E1ATP.     

Energy Expenditure Determined by Self-Reported Physical Activity Is Related to Body Fatness

BUCHOWSKI, MACIEJ S., KAREN M. TOWNSEND, KONG Y. CHEN, SARI A. ACRA, AND MING SUN. Energy expenditure determined by self-reported physical activity is related to body fatness. Obes. Res. 1999;7:23–33. Objective : Activity self-reports are a commonly used tool in assessing daily physical activity (PA) and associated energy expenditure (EE). This study examined the effect of relative body fatness (%BF) on differences between self-reported and measured duration and associated EE in healthy adults. Research Methods and Procedures: Men and women (n= 115, age 38±9 years), ranging in %BF from 7.9% to 58.9%, spent two separate days (normal and exercise) in a whole-room indirect calorimeter where EE was measured. While in the room calorimeter, subjects reported the type, intensity, and duration of each performed PA. The Compendium of Physical Activity was used to calculate the energy cost of each reported activity. The EE of all self-reported activities (EE_r) was categorized into four intensity levels, synchronized, and compared with EE from the room calorimeter (EE_m). Results : With increasing %BF, subjects significantly overestimated duration of more strenuous activities (≥4.5), while underestimating moderate activities (2.5 to 4.4 metabolic equivalents (METs)). Misreporting of duration and/or intensity caused an overestimation or underestimation of PA-associated EE at these levels. Reported EE sleep was lower than measured EE sleep, although both had similar durations. As a result, total EE_r was similar to EE_m. Discussion : Individual variability of daily total PA and associated EE generated from self-reports in adults is high. Persons with a higher %BF report duration and/or intensity of moderate to high levels of PA with lower accuracy than leaner individuals. We conclude using the Compendium of Physical Activity is not suitable for the accurate estimation of self-reported EE of AA in adults with a higher %BF.     

Role of a mitogen-activated protein kinase pathway in the induction of phase II detoxifying enzymes by chemicals.

Mitogen-activated protein kinase (MAPK) cascades are activated by diverse extracellular signals and participate in the regulation of an array of cellular programs. In this study, we investigated the roles of MAPKs in the induction of phase II detoxifying enzymes by chemicals. Treatment of human hepatoma (HepG2) and murine hepatoma (Hepa1c1c7) cells with tert-butylhydroquinone (tBHQ) or sulforaphane (SUL), two potent phase II enzyme inducers, stimulated the activity of extracellular signal-regulated protein kinase 2 (ERK2) but not c-Jun N-terminal kinase 1. tBHQ and SUL also activated MAPK kinase. Inhibition of MAPK kinase with its inhibitor, PD98059, abolished ERK2 activation and impaired the induction of quinone reductase, a phase II detoxifying enzyme, and antioxidant response element (ARE)-linked reporter gene by tBHQ and SUL. Overexpression of a dominant-negative mutant of ERK2 also attenuated tBHQ and SUL induction of ARE reporter gene activity. Interestingly, although expression of Ras and its mutant forms showed distinct effects on basal ARE reporter gene activity, they did not affect the activation of reporter gene by the inducers. Furthermore, a dominant-negative mutant of Ras had little effect on ERK2 activation by tBHQ and SUL, implicating a Ras-independent mechanism. Indeed, both tBHQ and SUL were able to stimulate Raf-1 kinase activity in vivo as well as in vitro. Thus, our results indicate that the induction of ARE-dependent phase II detoxifying enzymes is mediated by a MAPK pathway, which may involve direct activation of Raf-1 by the inducers.     

Cytological Observations of Microsporogenesis and Pollen Development in Triticum Sect. Trititrigia,T. aestivum and Their Hybrids

Cytological observation of microsporogenesis and pollen development of two parents, Xiaoyan 7430 and Yannong 15, and their hybrids were carried out by using squash method in this study. The results show: that microsporogenesis of the two parents, Xiaoyan 7430 and Yannong 15, is normal but their microspores usually aborted at first meiosis in pollen development. The frequency of abortion is higher in the former than the latter. However, the pollen development of which passed through the first meiosis is normal at the 2- or 3-nucleated stage. The rate of setting of both parents is basically normal. The meiosis of pollen mother cell (PMC) of two hybrids of Xiaoyan 7430 × Lumai No.1 and Xiaoyan 7430 × Yannong 15 is quite chaotic. Despite of the high frequency of univalents and multivalents at meiotic MI of PMC, and of micronucleoli in tetrad as well of the laggards at meiotic Al observed, the frequency of abortion of microspore are both at about 10%, similar to that of Xiaoyan 7430, at first meiosis of microspore in the stage of pollen development. Even though the pollen developments are basically normal in the 2- or 3-nucleated stage, but the percentage of setting of two hybrids is 28.24% and 33.82% respectively, apparently lower than that of their parents. The above-mentioned results indicate that although meiosis of PMC of F1 is chaotic, yet normal microspore could be formed and stages of pollen development cart still be carried on. The lower seed setting of F1 is not mainly due to abortion of pollen.     

Characteristics of Plant Communities and Element Contents in Plants at Mengentaoligai Ag,Pb, Zn Mine area in Inner Mongolia

The types of plant communities in Mengentaoligai mine area are disscussed. Arenaria juncea, densely grown in the phytocommunities of the mineralized zone, is found closely related to the presence of Pb and Zn mineral deposits. Analytical results of seven element contents (in ash) for 34 species (or part of plant) show that: levels of element contents in sequence in. the plants are Fe>Mn > Zn > Pb > Cu > Ni>Co; variable ranges of element contents in the plants are Pb, Zn>Fe,Mn> Cu> Co > Ni; and variable ranges of Pb, Zn contents in the same species at different sites are respectively larger than that among species. For example, Pb and Zn contents of Arenaria juncea, l145ppm and 3087ppm respectively, are the highest; the difference among Pb contents of Ulmus macrocarpa, Arenaria ?uncea and PotentiUa chinensis at different sites are more than 10 folds. The difference of Co and Ni contents in the species is less than two to one- Striking correlation is found between elements in plants and in soils, such as the Pb and Zn contents between leaves and twigs of Ulmus macrocarpa, twigs of Prunus sibirica, Artemisia halodendron and soils (lrl≤α 0.05 or≤α 0.01). It is found that Pb and Zn phytogeochemical anomalies, correlate closely with Pb and Zn mining deposits. In addition, analysis of principal component was conducted among seven elements contents of 14 species (or part of plant) in the mineralized zone and 12 species in the unmineralized zone.     

云南省可培养丝孢真菌资源的调查研究Ⅱ

本文继续报道曲霉属的16个分类群：杂色曲霉原变种,杂色曲霉疣梗变种,聚多曲霉,焦曲霉,土曲霉原变种,土曲霉金色变种,黄柄曲霉,温特曲霉,黄曲霉原变种,黄曲霉柱头变种,溜曲霉,炭黑曲霉,黑曲霉,泡盛曲霉,塔宾曲霉和日本曲霉。