Microcalorimetric study of Escherichia coli growth inhibited by the selenomorpholine complexes

The inhibitory or antibiotic action of four kinds of the selenomorpholine complex on a strain of Escherichia coli was studied by microcalorimetry. Differences in their capacities to inhibit the metabolism of this bacterium were observed. The extent and duration of the inhibitory effect on the metabolism as judged from the rate constant, k, and the half-inhibitory concentration, IC₅₀, varied with the different drugs. The rate constant (k) of Escherichia coli (in the log phase) in the presence of the drugs decreased with increasing concentrations of the drugs (C). The relationship of k and C is nearly linear for (1) selenomorpholine and (2) selenomorpholine hydrochloride, but for (3) N,N′-methylene bisselenomorpholine and (4) N-dodecyl selenomorpholine, it is not linear. The experimental results reveal that the sequence of antibiotic activity of selenomorpholines is (3) and (4)>(1)>(2).     

A microcalorimetric method for studying the biological effects of La(3+) on Escherichia coli

A microcalorimetric technique based on the bacterial heat-output was explored to evaluate the stimulatory effect of La(3+) on Escherichia coli. The power-time curves of the growth metabolism of E. coli and the effect of La(3+) on it were studied using an LKB-2277 BioActivity Monitor, stopped-flow method, at 37 degrees C. For evaluation of the results, the maximum power (P(max)), the growth rate constants (k) and the heat effects (Q(LOG), Q(STAT)) for the log phase, the stationary phase and the total heat effect (Q(T)) for E. coli were determined. The microcalorimetric method agreed with the conventional methods, such as cell numbers and biomass. La(3+) in the concentration ranges of 0-400 microg/ml has stimulatory effects on E. coli, while La(3+) ion of higher concentrations (>400 microg/ml) can inhibit the growth. This phenomenon is very similar to those observed from the in vitro cells and tissues from animals, plants and some microorganisms by other methods.     

Microcalorimetric investigation of the toxic action of Cd(2+) on Rhizopus nigricans growth

The microcalorimetric bioassay for acute cellular toxicity is based on metabolic heat production from cultured cells. Microcalorimetry is a quantitative, inexpensive, and versatile method for toxicology research. The biological response to toxicants is the inhibition of the heat production rate in cells and toxicity is expressed as the concentration of toxicant that is 50% effective in this inhibition (IC(50)). In this paper, the effect of Cd(2+) on Rhizopus nigricans growth was investigated at 25 degrees C. The relationship between growth rate constants (k) and concentration of Cd(2+) (C) shows a logarithmic normal distribution, and described as k=1. 2742x10(61)exp[-1.810x10(-3)(C+283.0)(2)], and IC(50) is 0.72 microg/ml. These signals are readily obtained by an LKB 2277-204 heat conduction microcalorimeter.     

ADP-Glucose Pyrophosphorylase Is Localized to Both the Cytoplasm and Plastids in Developing Pericarp of Tomato Fruit

The intracellular location of ADP-glucose pyrophosphorylase (AGP) in developing pericarp of tomato (Lycopersicon esculentum Mill) has been investigated by immunolocalization. With the use of a highly specific anti-tomato fruit AGP antibody, the enzyme was localized in cytoplasm as well as plastids at both the light and electron microscope levels. The immunogold particles in plastids were localized in the stroma and at the surface of the starch granule, whereas those in the cytoplasm occurred in cluster-like patterns. Contrary to the fruit, the labeling in tomato leaf cells occurred exclusively in the chloroplasts. These data demonstrate that AGP is localized to both the cytoplasm and plastids in developing pericarp cells of tomato.     

Purification of ornithine carbamoyltransferase from kidney bean (Phaseolus vulgaris L.) leaves and comparison of the properties of the enzyme from canavanine-containing and -deficient plants

Kidney bean (Phaseolus vulgaris L.) ornithine carbamoyltransferase (OCT; EC 2.1.3.3) was purified to homogeneity from leaf homogenates in a single-step procedure, using δ-N-(phosphonoacetyl)-l-ornithine-Sepharose 6B affinity chromatography. The 8540-fold-purified OCT exhibited a specific activity of 526 micromoles citrulline per minute per milligram of protein at 35 °C and pH 8.0. The enzyme represents approximately 0.01% of the total soluble protein in the leaf. The molecular mass of the native enzyme was approximately 109 kDa as estimated by Sephacryl S-200 gel filtration chromatography. The purified protein ran as a single band of molecular mass 36 kDa when subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis and at a single isoelectric point of 6.6 when subjected to denaturing isoelectric focusing. These results suggest that the enzyme is a trimer of identical subunits. Among the tested amino acids, l-cysteine and S-carbamoyl-l-cysteine were the most effective inhibitors of the enzyme. The OCT of kidney bean showed a very low activity towards canaline. The OCTs of canavanine-deficient plants have very low canaline-dependent activities, but the OCTs of canavanine-containing plants showed high canaline-dependent activities. It was assumed that the substrate specificity of this enzyme determines the canavanine synthetic activity of the urea cycle. Received: 22 July 1997 / Accepted: 4 December 1997     

番茄抗病基因Cf9的3′UTR区含有内含子序列

从番茄（ＬｙｃｏｐｅｒｓｉｃｏｎｅｓｃｕｌｅｎｔｕｍＭｉｌ．）抗病品种“中杂９号”基因组ＤＮＡ中扩增并克隆了番茄抗叶霉病基因Ｃｆ９。序列分析结果表明,该基因全长２７５１ｂｐ,含有一个编码８６３个氨基酸的开放阅读框架。在该基因的３′ＵＴＲ区发现了一段未曾报道的内含子序列,长１１５ｂｐ,它所处的位置与番茄另一个抗叶霉病基因Ｃｆ２内含子的位置相似,其５′和３′边界序列为一重复序列,ＴＣＣＡＧＧ（Ｔ）ＡＴＴＣ,并与Ｃｆ２基因内含子边界序列高度同源。与已报道的Ｃｆ９的ｃＤＮＡ序列相比,它的第３７１位的核苷酸Ｔ突变成了Ｃ,从而使其编码蛋白的ＬＲＲ区第１２１位的亮氨酸突变为脯氨酸。     

The use of neamine as a molecular template: Identification of active site residues in the bacterial antibiotic resistance enzyme aminoglycoside 3′-phosphotransferase type IIa by mass spectroscopy

Four novel aminoglycoside-based affinity inactivators were shown to covalently modify the active site of aminoglycoside 3′-phosphotransferase type IIa (APH(3′)-IIa), an important resistance factor in bacteria for aminoglycoside antibiotics. Standard peptide mapping techniques failed with this enzyme. A novel mass spectroscopic analysis which combines protease digestion on the instrument probe, followed by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is described which permitted rapid identification of the sites of protein modification. By this new technique, Glu-3 and Asp-23 were identified as active-site residues, the side chains of which potentially may serve as counter ions for the ammonium functionalities at positions 6′, and 1 and 3 of the antibiotic substrates, respectively. These findings contradict previous assertions that the C-terminal third of the enzyme should form the active site, by placing the active site clearly in the N-terminal portion of the enzyme.     

近金线属的分类地位及金线属的鉴别特征(鲤形目:鲤科:亚科)

本文根据系统学原理,提出了建立新类元的依据;并据此从分类和系统发育上论证了近金线属ＡｎｃｈｉｃｙｃｌｏｃｈｅｉｌｕｓＬｉｅｔＬａｎ独立成属的可能性,认为应将近金线属归于金线属;修订了金线属ＳｉｎｏｃｙｃｌｏｃｈｅｉｌｕｓＦａｎｇ的鉴别特征。     

不同理化因子对雪莲培养细胞中黄酮类形成的影响

研究了不同理化因子对水母雪莲(Saussurea medusa Maxim)愈伤组织生长及黄酮类化合物生物合成的影响。结果表明,有利于细胞生长及黄酮形成的合适温度为25℃。白光对愈伤组织生长无促进作用,但有利于黄酮的形成。培养基中添加1mg／L NAA和O．2mg／L的KT组合对细胞的生长较有促进作用。5％蔗糖和1％葡萄糖的组合有利于细胞的生长和黄酮的形成。用⁶⁰C0-γ射线辐照愈伤组织,在剂量为4000Gy的条件下,获得一个合成黄酮能力高于原愈伤组织70％的细胞系。用高效液相和紫外分光光度法,测定离体培养光照条件下干细胞总黄酮的含量为3．2％,是暗培养的4．4倍。培养温度25℃时干细胞黄酮的含量为2．02％,分别为20℃,35℃时的5倍和3．2倍。