Theory of multivalent binding in one and two-dimensional lattices

Ligand binding to a linear lattice composed of N sites, under general conditions of cooperativity and number of sites covered upon binding, m, is approached in terms of the theory of contracted partition functions. The partition function of the system obeys a recursion relation leading to a generating function that provides an exact analytical solution for any case of interest. Site-specific properties of the lattice are derived from simple transformations of the analytical expressions. The McGhee-von Hippel model is obtained as a special case in the limit N --> infinity. The derivation is straightforward and involves no combinatorial arguments. Partition functions and site-specific properties are also derived for the case of non-cooperative binding to a two-dimensional torus of length N, containing s sites in its section for a total of sN sites. The torus provides a relevant model for ligand binding to double-stranded DNA (s = 2) or protein helices (s = 3,4). It is proved that non-cooperative binding to the two-dimensional torus can mimic cooperative binding to a one-dimensional linear lattice when m = s. The dimensional embedding of the lattice and the geometry of interaction of its sites play a crucial role in defining the binding properties of the system accessible to experimental measurements. Hence, caution must be exercised in the interpretation of Scatchard plots in terms of the one-dimensional McGhee-von Hippel model, especially when m < or = 4 and the geometry of the system is clearly two-dimensional.     

Keratella distribution in North Patagonian lakes (Argentina)

The distribution of Keratella species from 15 different lakes in North Patagonia (Argentina) was analysed. The genus was not present at altitudes above 1000 m. K. tropica was restricted to Patagonian Plateau lakes with a comparatively high conductivity. A morphometric analysis of the widely distributed K. cochlearis was performed. Results showed three groups of K. cochlearis corresponding to Andean lakes, Patagonian Plateau lakes and a Patagonian Reservoir.     

Aquatic Oligochaeta in Italy, with special reference to Naididae

We present a list of Italian freshwater and marine Oligochaeta in the families Lumbriculidae, Haplotaxidae, Tubificidae, Naididae, Propappidae, Criodrilidae, and Lumbricidae, representing 57 genera and 130 species. Published data reflect the incomplete knowledge of the Italian oligochaete fauna, restricted to certain geographical areas. Subterranean aquatic and marine fauna are of particular interest as these have been studied the least. We provide a comprehensive review of the Naididae including, for the first time, southern Italy and the islands of Sicily and Sardinia. The distribution of species is discussed and taxonomic problems arising from the morphological variability of Italian material are examined.     

A组轮状病毒SA11VP6基因的克隆和表达

从ＳＡ１１ＶＰ６基因全序列克隆开始,设计一对两端带有酶切位点的引物,逆转录ＰＣＲ扩增出ＶＰ６全基因ＣＤＮＡ。经酶切后插入ＰＵＣ１９,构建了ＶＰ６全基因克隆ＰＲＡ６。再经酶切后插入痘苗病毒载休质凿ＰＪＳＡ１１７５中。利用Ｌｉｐｏｆｅｃｔｉｎ导入ＴＫ１４３细胞,利用ＴＫ基因和Ｌａｃ基因作为重组病毒的筛选标记。表达产物用单克隆抗体ＥＬＩＳＡ法检测,发现细胞培养上清和细胞裂解液都是阳性。Ｗｅｓｔｅｒｎ ｂ     

Bioconversion of substituted naphthalenes to the corresponding salicylic acids

The Pseudomonas fluorescens N3 was isolated from soil for its ability to utilize naphthalene as a carbon source. The strain transforms 2,3-dimethyl-, 2-methoxy-, 1- and 2-ethylnaphthalenes to the corresponding salicylic acids competitively with chemical synthesis. The identification of 2-hydroxy-2-carboxy-7-ethylchromane by biotransformation of 2-ethylnaphthalene, contributes to elucidating the steps involved in the catabolic pathways of naphthalenes to salicylaldehydes. Correspondence to: F. Pelizzoni     

Compartmentalization of SHC, GRB2 and mSOS, and hyperphosphorylation of Raf-1 by EGF but not insulin in liver parenchyma.

Rat liver parenchyma harbors equal numbers of epidermal growth factor (EGF) and insulin receptors. Following administration of a saturating dose of EGF (10 micrograms/100 g body weight), there was a rapid (t1/2 approximately 1.1 min) internalization of receptor coincident with its tyrosine phosphorylation at residue 1173 and receptor recruitment of the adaptor protein SHC, its tyrosine phosphorylation and its association with GRB2 and the Ras guanine nucleotide exchange factor, mSOS, largely in endosomes. This led to a cytosolic pool of a complex of tyrosine-phosphorylated SHC, GRB2 and mSOS. It was demonstrated that these constituents were linked to Ras activation by the characteristic decrease in Raf-1 mobility on SDS-PAGE, which was maintained for 60 min after a single bolus of administered EGF. While insulin administration (15 micrograms/100 g body weight) led to insulin receptor beta-subunit tyrosine phosphorylation and internalization, there was little detectable tyrosine phosphorylation of SHC, recruitment of GRB2, association of a complex with mSOS or any detectable change in the mobility of Raf-1. Therefore, in normal physiological target cells in vivo, distinct signaling pathways are realized after EGF or insulin receptor activation, with regulation of this specificity most probably occurring at the locus of the endosome.     

An oxygenation-sensitive dye binding to Carcinus maenas hemocyanin

The interaction of 4',6-diamidino-2-phenylindole (DAPI) with Carcinus maenas hemocyanin has been investigated by steady state fluorescence, dynamic fluorescence and circular dichroism measurements. The dye binds to apohemocyanin (without copper) as well as to oxygenated hemocyanin and to deoxygenated hemocyanin with very similar affinities (kd approximately equal to 1 microM ) and number of binding sites (one per subunit). In contrast, the fluorescence quantum yield enhancement of DAPI bound to oxygenated hemocyanin is nearly 60% lower than that observed for deoxygenated and apo forms. The decrease of fluorescence of the dye bound to deoxygenated hemocyanin is a sigmoidal function of the oxygen partial pressure, specular to that observed by following the absorbance of the copper-oxygen charge transfer band at 340 nm. This result provides preliminary evidence that DAPI may be used as a functional probe to monitor the cooperative binding of oxygen to the protein. The higher fluorescence quantum yield of DAPI bound to either apohemocyanin or deoxygenated protein is characterized by a single fluorescence decay with lifetime of about 3 ns, while with the oxygenated protein two components of about 1 ns and 3.0 ns are observed. This result is interpreted assuming the existence of two rotamers of DAPI in solution (Szabo et al. Photochem. Photobiol. 44 (1986) 143-150) both able to interact with oxygenated hemocyanin but only one to deoxygenated and apo forms. We conclude that the different fluorescence behaviour of the dye induced by the presence of oxygen bound to the protein is probably due to a structural change of hemocyanin in cooperative interaction with oxygen. Furthermore, the interaction is confirmed by the induced negative ellipticity of DAPI bound to apohemocyanin and deoxy-hemocyanin and by the increase of fluorescence anisotropy of DAPI bound to all forms of protein investigated.     

Thermodynamic basis of site-specific cooperativity

Cooperative phenomena in biological macromolecules arise from the interaction of many distinct subsystems, such as structural domains or binding sites. Cooperative properties of the system as a whole, like protein folding or allosteric transitions, are subject to the restrictions imposed by thermodynamic stability. These restrictions, however, do not apply in the case of individual subsystems open to interactions with the rest of the macromolecule. The site-specific properties of such subsystems can be understood in general thermodynamic terms from those of a multicomponent system under particular conditions. The analogy provides a thermodynamic basis for site-specific Cooperativity. © 1994 John Wiley & Sons, Inc.