Impact of flooding on the densities of selected aquatic insects

Data from a four-year study of five aquatic insect species,Hydropsyche betteni, H. morosa, H. bronta, Isonychia bicolor, andEphoron leucon, were utilized to evaluate the impact of a 60-year flood and a few lesser floods. The survey began in August, 1984 and was terminated in October, 1987 with the 60-year flood occurring in November, 1985. Four sampling sites were established on the South River and six quantitative samples were taken each month from each site. Gauging stations on the South River provided accurate discharge data for the sampling sites and useful historical data. Densities for the five species were utilized in the evaluation of the floods. The importance of timing is pointed out, that is, floods that occur very close together or near the end of the life cycle of an insect make it difficult to evaluate floods as disturbances. The importance of life history traits, such as behavior and egg diapause, are discussed in respect to floods. Densities were reduced to less than 50% of their average values immediately after the 60-year flood for the threeHydropsyche spp. and at three sites forI. bicolor. Ephoron leucon showed no response to the 60-year flood. Densities of the four impacted species returned to previous levels in the following generation. The 60-year flood was considered a disturbance in the near term but not for more than one generation.     

Mutant Escherichia coli penicillin acylase with enhanced stability at alkaline pH

Increased stability at alkaline pH should be a valuable attribute for the utilization of penicillin acylase in bioreactors employed to convert penicillins into 6-aminopenicillanic acid, a precursor of semisynthetic penicillins. In these systems, base is added for pH control, which results in local alkaline conditions that promote enzyme inactivation. Hydrolysis and synthesis reactions are also pH dependent. Here, we report work in which the gene coding for Escherichia coli penicillin acylase was subjected to oligonucleotide-directed random mutagenesis at regions coding for amino acids predicted to be at the surface of the enzyme. The resulting mutant library, cloned in E. coli, was screened by a filter paper assay of the colonies for the presence of penicillin acylase activity with enhanced stability at alkaline pH. Characterization of one of the selected clones revealed the presence of a mutation, Trp431-Arg, which would presumably alter the surface charge of the protein. In vitro experiments demonstrated a near twofold increase in the half-life of the mutant enzyme when stored at pH 8.5 as compared with the wild-type enzyme, with a comparable specific activity at several pH values. In general, the mutant displayed increased stability toward the basic side in the pH-stability profile. (c) 1995 John Wiley & Sons, Inc.     

The role of context on alpha-helix stabilization: host-guest analysis in a mixed background peptide model.

The helix content of a series of peptides containing single substitutions of the 20 natural amino acids in a new designed host sequence, succinyl-YSEEEEKAKKAXAEEAEKKKK-NH2, has been determined using CD spectroscopy. This host is related to one previously studied, in which triple amino acid substitutions were introduced into a background of Glu-Lys blocks completely lacking alanine. The resulting free energies show that only Ala and Glu- prove to be helix stabilizing, while all other side chains are neutral or destabilizing. This agrees with results from studies of alanine-rich peptide modela, but not the previous Glu-Lys block oligomers in which Leu and Met also stabilize helix. The helix propensity scale derived from the previous block oligomers correlated well with the frequencies of occurrence of different side chains in helical sequences of proteins, whereas the values from the present series do not. The role of context in determining scales of helix propensity values is discussed, and the ability of algorithms designed to predict helix structure from sequence is compared.     

Design of a leucine zipper coiled coil stabilized 1.4 kcal mol-1 by phosphorylation of a serine in the e position.

Using a dimeric bZIP protein, we have designed a leucine zipper that becomes more stable after a serine in the e position is phosphorylated by protein kinase A (delta delta GP = -1.4 kcal mol-1 dimer-1 or -0.7 kcal mol-1 residue-1). Mutagenesis studies indicate that three arginines form a network of inter-helical (i,i' + 5; i, i' + 2) and intra-helical (i, i + 4) attractive interactions with the phosphorylated serine. When the arginines are replaced with lysines, the stabilizing effect of serine phosphorylation is reduced (delta delta GP = -0.5 kcal mol-1 dimer-1). The hydrophobic interface of the leucine zipper needs a glycine in the d position to obtain an increase in stability after phosphorylation. The phosphorylated protein binds DNA with a 15-fold higher affinity. Using a transient transfection assay, we document a PKA dependent four-fold activation of a reporter gene. Phosphorylation of a threonine in the same e position decreases the stability by delta delta GP = +1.2 kcal mol-1 dimer-1. We present circular dichroism (CD) thermal denaturations of 15 bZIP proteins before and after phosphorylation. These data provide insights into the structural determinants that result in stabilization of a coiled coil by phosphorylation.     

生物实验数据的某些非线性分析方法

简要介绍常用的非线性动力学参量,结合生物学实验数据的特点,给出几种最新的分析方法.     

枯草杆菌蛋白酶E的156和165位突变

应用定点突变方法,在M222A突变的枯草杆菌蛋白酶E基因上进行E156S和V165I定点突变. 将突变基因插入大肠杆菌-枯草杆菌穿梭质粒pBE-2中,在碱性和中性蛋白酶缺陷型的枯草杆菌DB104中进行表达,得到突变种(M222A,E156S)和(M222A,E156S,V165I)蛋白酶E. 性质测定表明,E156S突变使蛋白酶比活力增加90%,并不影响酶的热稳定性和抗氧化性. 而V165I突变使蛋白酶比活力降低.     

兔感觉神经特异蛋白的纯化及稳定性观察

以兔脊神经节及背根纤维为材料,通过制备匀浆,DEAE-Sephacel阴离子交换层析,高压液相凝胶过滤层析分离纯化了感觉神经特异蛋白29 ku,并进行了该蛋白的稳定性观察.     

Global stability of an SIR epidemic model with time delays

An SIR disease transmission model is formulated under the assumption that the force of infection at the present time depends on the number of infectives at the past. It is shown that a disease free equilibrium point is globally stable if no endemic equilibrium point exists. Further the endemic point (if it exists) is globally stable with respect to the whole state space except the neighborhood of the disease free state.Research partly supported by the Ministry of Education, Science and Culture, Japan, Grant 05640256