Artificial metalloenzymes for enantioselective catalysis based on biotin-avidin

Homogeneous and enzymatic catalysis offer complementary means to generate enantiomerically pure compounds. Incorporation of achiral biotinylated rhodium-diphosphine complexes into (strept)avidin yields artificial metalloenzymes for the hydrogenation of N-protected dehydroamino acids. A chemogenetic optimization procedure allows one to produce (R)-acetamidoalanine with 96% enantioselectivity. These hybrid catalysts display features reminiscent both of enzymatic and of homogeneous systems.     

Artificial metalloenzymes: (strept)avidin as host for enantioselective hydrogenation by achiral biotinylated rhodium-diphosphine complexes

We report on the generation of artificial metalloenzymes based on the noncovalent incorporation of biotinylated rhodium-diphosphine complexes in (strept)avidin as host proteins. A chemogenetic optimization procedure allows one to optimize the enantioselectivity for the reduction of acetamidoacrylic acid (up to 96% ee (R) in streptavidin S112G and up to 80% ee (S) in WT avidin). The association constant between a prototypical cationic biotinylated rhodium-diphosphine catalyst precursor and the host proteins was determined at neutral pH: log K(a) = 7.7 for avidin (pI = 10.4) and log K(a) = 7.1 for streptavidin (pI = 6.4). It is shown that the optimal operating conditions for the enantioselective reduction are 5 bar at 30 degrees C with a 1% catalyst loading.     

Inégalités de Harnack pour les solutions d'équations du type courbure scalaire prescrite

We prove some a priori estimates in dimension $n?2$ for equations of type prescribed scalar curvature. In the particular case of the unit sphere ${\mathbb{S}}_2$ we give an estimation of the constant c in the inequality ${\sup }_{{\mathbb{S}}_2}u+{\inf }_{{\mathbb{S}}_2}u?c$. To cite this article: S. Skander Bahoura, C. R. Acad. Sci. Paris, Ser. I 341 (2005).     

Increasing antigenicity of B16 melanoma cell fraction with microwave hyperthermia

An injection of a fraction of a fraction (C30 mw) obtained by centrifugation at 30 kg of homogenate of B16 melanoma cells, treated with microwave hyperthermia (2450 MHz, CW, 44 degrees C, for 20 minutes), increases the survival time (p less than 0.01) of C57-BL/6J male mice inoculated 26 days later with 10(7) cells (viability greater than 95%) of B16 melanoma. This delay of 26 days between these two injections corresponds to the moment where the synthesis of immunoglobulins is increased in protected mice. The earliest death (p less than 0.001) of animals injected with untreated tumoral cell fraction (C30), and that received a suspension of viable B16 melanoma cells (10(7)) can be explained by an inhibition of humoral immunity system.     

A fast method to block-diagonalize a Hankel matrix

In this paper, we consider an approximate block diagonalization algorithm of an n×n real Hankel matrix in which the successive transformation matrices are upper triangular Toeplitz matrices, and propose a new fast approach to compute the factorization in O(n ²) operations. This method consists on using the revised Bini method (Lin et al., Theor Comp Sci 315: 511–523, 2004). To motivate our approach, we also propose an approximate factorization variant of the customary fast method based on Schur complementation adapted to the n×n real Hankel matrix. All algorithms have been implemented in Matlab and numerical results are included to illustrate the effectiveness of our approach.     

Inégalités de Harnack pour les opérateurs elliptiques d'ordre 2 et 4 et phénomène de concentration

We give some results concerning $\sup \times \inf$ inequalities for some elliptic operators of order 2 and 4. With those inequalities and the concentration phenomena we can describe the asymptotic behavior of those PDE solutions. To cite this article: S.S. Bahoura, C. R. Acad. Sci. Paris, Ser. I 342 (2006).     

A straightforward methodology to overcome solubility challenges for N-terminal cysteinyl peptide segments used in native chemical ligation

One of the main limitations encountered during the chemical synthesis of proteins through native chemical ligation (NCL) is the limited solubility of some of the peptide segments. The most commonly used solution to overcome this problem is to derivatize the segment with a temporary solubilizing tag. Conveniently, the tag can be introduced on the thioester segment in such a way that it is removed concomitantly with the NCL reaction. We herein describe a generalization of this approach to N-terminal cysteinyl segment counterparts, using a straightforward synthetic approach that can be easily automated from commercially available building blocks, and applied it to a well-known problematic target, SUMO-2.

We herein describe a straightforward approach for the introduction of a solubilizing tag on N-terminal cysteinyl segments used in native chemical ligation-based protein chemical synthesis. Conveniently, the tag is removed during the ligation.     

LOWER BOUNDS FOR SUP＋INF AND SUP＊INF AND AN EXTENSION OF CHEN-LIN RESULT IN DIMENSION 3

We give two results about Harnack type inequalities. First, on Riemannian surfaces, we have an estimate of type sup ＋ inf. The second result concern the solutions of prescribed scalar curvature equation on the unit ball of Rn with Dirichlet condition. Next, we give an inequality of type （supK ^u）^2s-1 × infπu ≤ c for positive solutions of △u = V u^5 on Ω belong toR^3, where K is a compact set of Ω and V is s-Holderian, s ∈] - 1/2, 1]. For the case s = 1/2 and Ω = S3, we prove that, if minΩ u 〉 m 〉 0 （for some particular constant m 〉 0）, and the H¨olderian constant A of V tends to 0 （in certain meaning）, we have the uniform boundedness of the supremum of the solutions of the previous equation on any compact set of Ω.