Publications by authors named "Loffet A"

The 96-amino acid protein Vpr functions as a regulator of cellular processes involved in the human immunodeficiency virus, type 1 (HIV-1) life cycle, including cell-cycle arrest at the G2/M check point, promotion of the HIV-1 preintegration complex for nuclear transport, induction of apoptosis and transcriptional activation of a variety of viral and cellular promoters. Preliminary 1H NMR experiments performed on Vpr fragments showed the presence of several helical regions. However, the assignment of many protons in the amide region of the complete sequence of Vpr proved to be impossible due to the overlap of multiple NOE cross peaks.

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N-Urethane-protected N-carboxyanhydrides (UNCAs) are very reactive amino acid derivatives. They have been successfully used in peptide synthesis, in both solution and solid phase. We have demonstrated that UNCAs are interesting starting materials for the synthesis of various amino acid derivatives.

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Allyl and allyloxycarbonyl groups are used for the side-chain protection of amino acids. The protecting groups may be selectively cleaved using the reagent HSnBu3 under palladium catalysis. The preparation of Boc and Fmoc series of protected amino acids is described.

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Ten phenylthiohydantoin (PTH) amino acids possessing allyl (Al) or allyloxycarbonyl (Aloc) side-chain-protecting groups have been characterized by high-performance liquid chromatography for use in Edman degradation sequence analysis. Optimized separation of side-chain-protected and -unprotected PTH amino acids was achieved on a C-18 reversed-phase column with a two-step gradient spanning 32 min. Five of the side-chain-protected amino acids [Cys(Al), Cys(Aloc), Lys(Aloc), Thr(Aloc), Tyr(Al)] were completely stable to the conditions of PTH derivatization, four [Asp(OAl), Arg(Aloc)2, Glu(OAl), Ser(Aloc)] were partially deprotected during PTH derivatization, and one [His(Aloc)] was completely deprotected during PTH derivatization.

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The steady-state kinetic parameters of the tripeptides D-Val-Leu-Lys-, Ala-Phe-Lys-, and < Glu-Phe-Lys- in which the free carboxyl group was substituted with p-nitroaniline (substrate) or chloromethane (inhibitor), towards the serine proteinases plasmin (EC 3.4.21.

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Serine is one of the enzyme residues with which benzylpenicillin collides as a result of its binding to the Streptomyces strain-R61 DD-carboxypeptidase-transpeptidase enzyme. Nucleophilic attack occurs on C(7) of the bound antibiotic molecule with formation of a benzylpenicilloyl-serine ester linkage, i.e.

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The efficiency of energy transfer between a fluorescent donor, L-tyrosine, and a fluorescent acceptor, L-tryptophan, has been determined in R'-L-Trp-L-Ala-L-Tyr-R", R-L-Trp-L-Ala-L-Ala-L-Tyr-R", and R'-L-Trp-Gly-L-Ala-L-Tyr-R" in ethanol solution. The protecting groups R' and R" were respectively tert-butyloxycarbonyl and methyl ester. A conformational theoretical analysis of molecules studied has been performed in parallel on the basis of semiempirical conformational potential energy function.

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