Changes in DNA supertwist as a response of Bacillus subtilis towards different kinds of stress

Abstract The silent parD ( kis/kid ) stability operon of plasmid R1 is normally repressed by the co-ordinated action of the Kis and Kid proteins. In this report it is shown that a mutation in repA , the gene of the plasmid replication protein, that reduces two-fold the copy number of the plasmid, leads to the derepression of the parD system. This derepression can be prevented by a suppressor mutation in copB, a copy number control gene of plasmid R1, that increases the efficiency of replication of the repA mutant. Derepression of the wild-type parD system leads to high plasmid stability. These data show the activation of a plasmid stability operon by a mutation that reduces the efficiency of wild-type plasmid replication.     

Mutations of surface residues in Anabaena vegetative and heterocyst ferredoxin that affect thermodynamic stability as determined by guanidine hydrochloride denaturation.

The stability properties of oxidized wild-type (wt) and site-directed mutants in surface residues of vegetative (Vfd) and heterocyst (Hfd) ferredoxins from Anabaena 7120 have been characterized by guanidine hydrochloride (Gdn-HCl) denaturation. For Vfd it was found that mutants E95K, E94Q, F65Y, F65W, and T48A are quite similar to wt in stability. E94K is somewhat less stable, whereas E94D, F65A, F65I, R42A, and R42H are substantially less stable than wt. R42H is a substitution found in all Hfds, and NMR comparison of the Anabaena 7120 Vfd and Hfd showed the latter to be much less stable on the basis of hydrogen exchange rates (Chae YK, Abildgaard F, Mooberry ES, Markley JL, 1994, Biochemistry 33:3287-3295); we also find this to be true with respect to Gdn-HCl denaturation. Strikingly, the Hfd mutant H42R is more stable than the wt Hfd by precisely the amount of stability lost in Vfd upon mutating R42 to H (2.0 kcal/mol). On the basis of comparison of the X-ray crystal structures of wt Anabaena Vfd and Hfd, the decreased stabilities of F65A and F65I can be ascribed to increased solvent exposure of interior hydrophobic groups. In the case of Vfd mutants E94K and E94D, the decreased stabilities may result from disruption of a hydrogen bond between the E94 and S47 side chains. The instability of the R42 mutants is also most probably due to decreased hydrogen bonding capabilities.(ABSTRACT TRUNCATED AT 250 WORDS)     

The distribution of alpha-helix propensity along the polypeptide chain is not conserved in proteins from the same family.

We address the question of whether the distribution of secondary structure propensities of the residues along the polypeptide chain (denominated here as secondary structure profiles) is conserved in proteins throughout evolution, for the particular case of alpha-helices. We have analyzed by CD the conformation of peptides corresponding to the five alpha-helices of two alpha/beta parallel proteins (ComA and Ara). The large alpha-helical population of peptide ComA-4 detected by CD in aqueous solution has been confirmed by NMR. These proteins are members of the CheY and P21-ras families, respectively, which have been studied previously in the same way (Muñoz V, Jiménez MA, Rico M, Serrano L, 1995, J Mol Biol 245:275-296). Comparison of the helical content of equivalent peptides reveals that protein alpha-helix propensity profiles are not conserved. Some equivalent peptides show very different helical populations in solution and this is especially evident in very divergent proteins (ComA and CheY). However, all the peptides analyzed so far adopted an important population of helical conformations in the presence of 30% trifluoroethanol, indicating that there could be a conserved minimal requirement for helical propensity.     

Superoxide dismutase mimetic activity of a cyclic tetrameric Schiff base N-coordinated Cu(II) complex

A pulse radiolytic study using the cyclic tetrameric Schiff base N-coordinated copper complex Cu(TAAB)²⁺ has been performed. The reaction of the Cu(TAAB)²⁺ complex with superoxide revealed pseudo first-order characteristics with the rate constant of k ₂ = (2.9 ± 0.5) × 10⁸ mol^–1 s^–1 dm³. The complex survive presence of competing serum albumin in physiological concentrations. The complex stability constant K = 1.15 × 10¹⁸ (log K = 18.06) is two orders of magnitude higher than that of Cu(II)-serum albumin (log K = 16.2). Transient changes of the stability during the oxidation/reduction process and in the presence of 600 /mol l^–1 albumin did not affect significantly either the electronic absorption of the complex or its catalytic activity.     

Taenia taeniaeformis: characterization of larval metabolic products and growth of host gastric cells in vitro

Development of larvae of the cestode parasite Taenia taeniaeformis in the liver of rats induces gross hyperplasia of the gastric mucosa and excessive mucus production in the stomach without any direct contact with the stomach. Because the taeniid larvae are known to elaborate excretory-secretory (E-S) product in vivo and in vitro, the product was analyzed further, and its effects on cultured rat and dog stomach cells were investigated. In vitro E-S product contained less negatively charged glycosaminoglycan than either heparin or chondroitin sulfate, and proteins of various molecular weights. It stimulated the growth of both rat and dog stomach cells at concentrations of 3-9 micrograms protein/ml culture medium. At a concentration of 30 micrograms protein/ml culture medium, it stimulated hexosamine production in the cells up to 20 times, and multiple intracytoplasmic granules were found in both rat and dog cultured cells by light and electron microscopy. These results suggest that larval E-S product may be involved in the induction of gastric hyperplasia and hypermucus secretion.     

Sucrose modifies ribosomal stability and conformation

High concentrations of sucrose have a strong protective effect on heat-induced modifications of rat liver ribosomal subunits. They prevent to a large extent subunit inactivation, measured by poly (U)-dependent [14C] Phe tRNA binding (40S subunits) and puromycin reaction (60S subunits), subunit unfolding into light forms, and the release of both free and protein-complexed 5S RNA. They also increase the temperature at which subunits start to melt. Our data indicate that sucrose affects subunit conformation.     

Enzyme activities in concentrated solutions of glycinebetaine and other solutes

The activities of a number of enzymes in concentrated solutions of glycinebetaine and other solutes have been studied. Glycinebetaine, in contrast to electrolytes such as NaCl, was found to be noninhibitory up to 500 mM. This is compatible with the postulated role of glycinebetaine in cytoplasmic osmoregulation. Partial protection against NaCl inhibition was afforded by glycinebetaine in some cases. More detailed studies on glycinebetaine —NaCl-enzyme interactions were carried out using malate dehydrogenase (decarboxylating) from Hordeum vulgare.Abbreviations TES N-tris[hydroxymethyl]methyl-2-aminoethane sulphonic acid - MES 2[N-Morpholino]ethane sulphonic acid     

Nutritional and karyotypic characterization of a haploid cell culture ofDaucus carota

Summary The purpose of this study was to optimize growth conditions for a strain of haploid carrot callus and to follow its karyotypic changes in a long span of time. The strain has been maintained in liquid suspension since September 1977. It has remained predominantly haploid in its karyotype since that time. The original explant was initiated and subsequently subcultured in Gamborg's B5 medium. The components of the B5 medium were omitted one at a time and sequentially added back to determine their minimum, optimum, and maximum nontoxic concentrations. These changes were made in the original formula: the addition of an organic buffering agent and an increase in the iron and other micronutrient concentrations. Using this slightly modified B5 medium, we assessed the effect on growth by single additions of amino acids, different carbon sources, growth regulators, and vitamins. No improvement in plating efficiency resulted from addition of any of these compounds. We conclude that there are factors limiting the plating efficiency of the haploid cells other than these tested, or that single additions will not make a discernible difference, or that growth promoting factors cannot be exogenously supplemented to cultured cells.     

一类含间隙分布时滞的种群增长模型的稳定性

本文首先利用间隙分布时滞函数来建立更为符合实际的种群增长模型,然后运用两种不同的方法,对其平衡位置的局部稳定性进行了全面的讨论,得出了局部渐近稳定的充分必要条件,在参数平面上划分出了稳定和不稳地的区域。     

Mechanism of insulin aggregation and stabilization in agitated aqueous solutions

Undesirable aggregation of aqueous insulin solutions remains a serious obstacle in the development of alternative methods of diabetes therapy. We investigated the fundamental nature of the aggregation mechanism and proposed stabilization strategies based on a mathematical model for the reaction scheme. Insulin aggregation kinetics in the presence of solid-liquid and air-liquid interfaces were monitored using UV spectroscopy and quasielastic light scattering (QELS). Experimental observations were consistent with our model of monomer denaturation at hydrophobic surfaces followed by the formation of stable intermediate species which facilitated subsequent macroaggregation. The model was used to predict qualitative trends in insulin aggregation behavior, to propose stabilization strategies, and to elucidate mechanisms of stabilization. In the absence of additives, insulin solutions aggregated completely (more than 95% of the soluble protein lost) within 24 h; with sugarbased nonionic detergents, no detectable loss occurred for more than 6 weeks. (c) 1992 John Wiley & Sons, Inc.