Comparison of Sepharose CL-2B and CL-4B Matrices in Purification of the Hepatitis B Surface Antigen by Affinity Chromatography

Sepharose CL-4B and Sepharose CL-2B with immobilized CB.Hep-1 monoclonal antibody were compared for studying the matrix efficiency in the immunopurification of the recombinant hepatitis B surface antigen (rHBsAg). The elution capacities of both matrices were similar over eight chromatographic cycles, significant differences were only observed in the first purification cycles. A high percentage of the adsorbed rHBsAg was not eluted from both matrices. The rHBsAg purity was not affected by matrix characteristics (pore size and percentage of agarose) and differences between Sepharose CL-4B and Sepharose CL-2B do not provoke differences in the antibody released from the matrices under defined experimental conditions.     

Some sufficient conditions for the existence of kernels in infinite digraphs

A kernel N of a digraph D is an independent set of vertices of D such that for every w∈V(D)−N there exists an arc from w to N. If every induced subdigraph of D has a kernel, D is said to be a kernel perfect digraph. D is called a critical kernel imperfect digraph when D has no kernel but every proper induced subdigraph of D has a kernel. If F is a set of arcs of D, a semikernel modulo F of D is an independent set of vertices S of D such that for every z∈V(D)−S for which there exists an (S,z)-arc of D−F, there also exists an (z,S)-arc in D. In this work we show sufficient conditions for an infinite digraph to be a kernel perfect digraph, in terms of semikernel modulo F. As a consequence it is proved that symmetric infinite digraphs and bipartite infinite digraphs are kernel perfect digraphs. Also we give sufficient conditions for the following classes of infinite digraphs to be kernel perfect digraphs: transitive digraphs, quasi-transitive digraphs, right (or left)-pretransitive digraphs, the union of two right (or left)-pretransitive digraphs, the union of a right-pretransitive digraph with a left-pretransitive digraph, the union of two transitive digraphs, locally semicomplete digraphs and outward locally finite digraphs.     

A sufficient condition for kernel perfectness of a digraph in terms of semikernels modulo F

A kernel of a directed graph is a set of vertices which is both independent and absorbent. And a digraph is said to be kernel perfect if and only if any induced subdigraph has a kernel. Given a set of arcs F , a semikernel S modulo F is an independent set such that if some Sz-arc is not in F , then there exists a zS-arc. A sufficient condition on the digraph is given in terms of semikernel modulo F in order to guarantee that a digraph is kernel perfect. To do that we give a characterization of kernel perfectness which is a generalization of a previous result given by Neumann-Lara [Seminúcleos de una digrfica. Anales del Instituto de Matemticas 2, Universidad Nacional Autónoma de México, 1971]. And moreover, we show by means of an example that our result is independent of previous known sufficient conditions.     

NMR and X‐ray crystallographic studies of linear and cyclic aminomethanephosphinates

We report the preparation of four diastereoisomeric pairs of ethyl {[(3‐hydroxypropyl)‐ amino](aryl)methyl}phenylphosphinates. In two cases, the phosphinates were transformed to 1,4,2‐oxazaphosphepane heterocycles through one‐pot intramolecular esterification. The analogous reaction with formaldehyde gave the six‐membered ethyl (1,3‐oxazinan‐3‐ylmethyl)phenylphosphinate, which could be transformed in a posterior reaction to the corresponding aminomethanephosphinic acid. The new compounds were characterized by IR, ¹H, ¹³C, and ³¹P NMR. © 2006 Wiley Periodicals, Inc. Heteroatom Chem 17:81–87, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20179     

Characterization of Costa Rican potsherds by neutron activation analysis

Neutron activation analysis has been applied to evaluate the concentrations of 24 elements in archaeological potsherds and 5 clay samples with a view of establishing the average composition profiles. Due to their stability in clays, 14 elements were selected as indicators. A statistical treatment of the overall analytical data, including principal component analysis, was applied in an attempt to determine correlations between the concentrations of the elements in the samples, possibly in relation with their ages and/or their places of collection.     

Elemental composition of lichens at Nahuel Huapi National Park,Patagonia, Argentina

Five species of epiphytic lichens were sampled from urban and periurban areas of Bariloche, a non industrial city located on the East side of the Nahuel Huapi National Park, North-Western Patagonia, Argentina, and from pristine areas of the Park. Each individual lichen was analyzed using Instrumental Neutron Activation Analysis. The results of the analysis showed high concentrations of lithophile elements, with very good correlations among them. The relative concentration of these elements in all lichen species is in good agreement with the elemental composition of sediments collected in the Park. Elemental concentrations which are not related to detritical inputs are also presented.     

A general model for non-autocatalytic zymogen activation in the presence of two different and mutually exclusive inhibitors. II. Relative weight of activation and inhibition processes

The kinetic study carried out in paper I of this series (preceding article) on enzyme systems involving zymogen activation and the simultaneous action of two different, mutually exclusive inhibitors (Scheme 1) allows, new dimensionless kinetic parameters to be suggested. These parameters furnish quantitative information about the relative weight of the activation and inhibition routes, i.e. the conditions under which the activation prevails over the inhibition and vice versa, as well as the absolute and relative contributions to overall inhibition of each of the inhibition routes and their synergistic effect. These results can be easily and directly applied to any of the thousands of particular cases of the model. Examples are given for different particular cases.     

Two forms of spiral-wave reentry in an ionic model of ischemic ventricular myocardium

It is well known that there is considerable spatial inhomogeneity in the electrical properties of heart muscle, and that the many interventions that increase this initial degree of inhomogeneity all make it easier to induce certain cardiac arrhythmias. We consider here the specific example of myocardial ischemia, which greatly increases the electrical heterogeneity of ventricular tissue, and often triggers life-threatening cardiac arrhythmias such as ventricular tachycardia and ventricular fibrillation. There is growing evidence that spiral-wave activity underlies these reentrant arrhythmias. We thus investigate whether spiral waves might be induced in a realistic model of inhomogeneous ventricular myocardium. We first modify the Luo and Rudy [Circ. Res. 68, 1501-1526 (1991)] ionic model of cardiac ventricular muscle so as to obtain maintained spiral-wave activity in a two-dimensional homogeneous sheet of ventricular muscle. Regional ischemia is simulated by raising the external potassium concentration ([K(+)](o)) from its nominal value of 5.4 mM in a subsection of the sheet, thus creating a localized inhomogeneity. Spiral-wave activity is induced using a pacing protocol in which the pacing frequency is gradually increased. When [K(+)](o) is sufficiently high in the abnormal area (e.g., 20 mM), there is complete block of propagation of the action potential into that area, resulting in a free end or wave break as the activation wave front encounters the abnormal area. As pacing continues, the free end of the activation wave front traveling in the normal area increasingly separates or detaches from the border between normal and abnormal tissue, eventually resulting in the formation of a maintained spiral wave, whose core lies entirely within an area of normal tissue lying outside of the abnormal area ("type I" spiral wave). At lower [K(+)](o) (e.g., 10.5 mM) in the abnormal area, there is no longer complete block of propagation into the abnormal area; instead, there is partial entrance block into the abnormal area, as well as exit block out of that area. In this case, a different kind of spiral wave (transient "type II" spiral wave) can be evoked, whose induction involves retrograde propagation of the action potential through the abnormal area. The number of turns made by the type II spiral wave depends on several factors, including the level of [K(+)](o) within the abnormal area and its physical size. If the pacing protocol is changed by adding two additional stimuli, a type I spiral wave is instead produced at [K(+)](o)=10.5 mM. When pacing is continued beyond this point, apparently aperiodic multiple spiral-wave activity is seen during pacing. We discuss the relevance of our results for arrythmogenesis in both the ischemic and nonischemic heart. (c) 1998 American Institute of Physics.     

A COMPARATIVE STUDY OF THE VISIBLE LIGHT PHOTOCHEMISTRY OF GILVOCARCINS V and M

Quantum yields for the formation of superoxide ions, O₂^?1, and singlet oxygen, ¹O₂, were determined during the photolyses of gilvocarcin M (GM) in air-saturated dry dimethylsulfoxide (DMSO) and in 45:55 (vol/vol) DMSO-water mixtures. The quantum yield for the photoreduction of methyl viologen by GM in nitrogen-saturated dry DMSO was also determined. These values are not different, within experimental error, from those corresponding to gilvocarcin V (GV). Because GV is a strong photocytotoxic agent and GM is not, these results imply that Type I and Type II mechanisms are not important pathways in the cytotoxicity of GV.