Varying patterns of protein synthesis in Drosophila during heat shock: Implications for regulation

The heat-shock response of Drosophila involves the vigorous induction of a small number of new messenger RNAs and proteins as well as the repression of most preexisting RNA and protein synthesis. The experiments presented here characterize the kinetics of messenger RNA and protein synthesis at different temperatures and the patterns of induction under a variety of culture conditions. In addition to providing practical information for further studies of the heat-shock response, the data provide some valuable insights into the nature of the response. In particular, the patterns of induction and repression are not simple functions of the degree of temperature elevation, but vary strikingly in different media and depend strongly upon the speed of the temperature increase. Several heat-shock proteins are shown to have very individual induction characteristics with respect to the temperatures at which they are maximally induced, the range of temperatures over which they are synthesized, and the kinetics of their induction. Thus, although this system has often been viewed as a simple, coordinate induction, it now appears that the various heat-shock genes can be, to a rather considerable extent, regulated independently of one another. The evidence further suggests that the patterns of protein synthesis in heat-shocked cells are regulated by mechanisms which act at several different levels of gene expression.     

The steady-state kinetics of isotope exchange for one substrate–one product enzymic reactions

Steady-state kinetic equations for isotope exchange are derived for a number of one substrate-one product enzymic mechanisms in which two molecules of substrate or product can be combined with an enzyme molecule at the one time (e.g. allosteric mechanisms). The usual assumption, that the radioactive material is distributed among the substrate and product components according to a first-order law, is not valid. One can recognize whether isotope-exchange kinetics of an enzyme reaction follows first-order behaviour by using various initial concentrations of the labelled substance added to a mixture.     

纸坊沟流域植被恢复区灌木林昆虫群落时间结构及动态

通过对纸房沟流域不同植被恢复区昆虫进行调查,结果表明:昆虫种类数以天然灌木林最高,混交林次之,单纯林分较低,个体数量以柠条林昆虫数量最高,其次为混交林和沙棘林,天然灌木林变化幅度最小。各植被昆虫种类和数量季节变化符合y=ax3 bx2 cx d函数变化规律。从特征指数来分析:昆虫群落多样性指数5～9月份大小次序均为天然灌木林>混交林>单纯林分,均匀度以单纯林和混交林的昆虫群落变化幅度较大,天然灌木林变化幅度最小。群落的优势度与均匀度值的变化呈相反趋势。主分量分析表明:植物类型不同的昆虫群落,其主导因素和时间格局不同,且结构越复杂,主导因素和时间格局越明显;相反,则主导因素和时间格局分化不明显;通过排序植食性昆虫、捕食性昆虫、寄生性昆虫在各植被昆虫群落变化的不同时期占主导因素。     

Effect of subunit dissociation, denaturation, aggregation, coagulation, and decomposition on enzyme inactivation kinetics: I. First-order behaviour

Enzyme inactivation kinetics typically follows what would appear to be simple first-order behavior. However, the inactivation process is known to involve a number of reversible (decomposition, denaturation) as well as irreversible (decomposition, aggregation, and coagulation) reactions. These reactions can combine to form a wide variety of reaction pathways which can potentially demonstrate complex inactivation kinetics. However, it was shown that with appropriate assumptions with regard to the relative magnitudes of the various reaction rates, many complex inactivation pathways can demonstrate apparent first-order behavior. Thus, with this analysis, a more accurate interpretation of the slope of an activity versus time semi-log plot can be obtained. (c) 1992 John Wiley & Sons, Inc.