L-Valyl-L-phenylalanine (Valylphenylalanine)

beta Turns, water cage formation and hydrogen bonding in the structures of L-valyl-L-phenylalanine

L-Valyl-L-phenylalanine has been crystallized as an orthorhombic dihydrate (1) in the shape of needles and as a monoclinic trihydrate (2) with Z = 16 (P2(1), Z' = 8) in the shape of thin plates. Peptide molecules in these two structures occur in three basic conformations, termed c(1), c(2A) and c(2B). c(2B) has not been observed previously for dipeptides. Together with c(1) it forms a model pair for Type I and Type II beta-turns in protein structures. The crystal packing of (2) is remarkable in that some of the L-Val side chains are exposed to the solvent region of the crystal rather than being located in a hydrophobic layer. The crystal packing thus offers a unique and detailed view of hydrogen-bond cage formation around the hydrophobic groups by the 24 cocrystallized water molecules. The eight [bond]NH(3)(+)...(-)OOC[bond] contacts in the structure are unusually short and the minimum N...O distance of 2.649 (5) A represents a new extreme limit for this type of hydrogen bond in peptide structures.

Synthesis and characterization of new polyamides derived from alanine and valine derivatives

Background: Many efforts have been recently devoted to design, investigate and synthesize biocompatible, biodegradable polymers for applications in medicine for either the fabrication of biodegradable devices or as drug delivery systems. Many of them consist of condensation of polymers having incorporated peptide linkages susceptible to enzymatic cleavage. Polyamides (PAs) containing α-amino acid residues such as L-leucine, L-alanine and L-phenylalanine have been reported as biodegradable materials. Furthermore, polyamides (PAs) derived from C10 and C14 dicarboxylic acids and amide-diamines derived from 1,6-hexanediamine or 1,12-dodecanediamine and L-phenylalanine, L-valyl-L-phenylalanine or L-phenylalanyl-L-valine residues have been reported as biocompatible polymers. We have previously described the synthesis and thermal properties of a new type of polyamides-containing amino acids based on eight new symmetric meta-oriented protected diamines derived from coupling of amino acids namely; Fomc-glycine, Fmoc-alanine, Fomc-valine and Fomc-leucine with m-phenylene diamine or 2,6-diaminopyridine. Results revealed that incorporation of pyridine onto the polymeric backbone of all series decreases the thermal stability.Here we describe another family of polyamides based on benzene dicarboxylic acid, pyridine dicarboxylic acid, and α-amino acid linked to benzidine and 4,4'-oxydianiline to study the effect of the dicarboxylic acid as well as the amino acids on the nature and thermal stability of the polymers.
Results: We report here the preparation of a new type of polyamides based on benzene dicarboxylic acid, pyridine dicarboxylic acid, and α-amino acid linked to benzidine and 4,4'-oxydianiline to study the effect of the dicarboxylic acid as well as the amino acids on the nature and thermal stability of polymers. The thermal properties of the polymers were evaluated by different techniques. Results revealed that structure-thermal property correlation based on changing the dicarboxylic acid monomer or the diamine monomer demonstrated an interesting connection between a single change (changing the dicarboxylic acids in each series while the diamine is fixed) and thermal properties. The newly prepared polymers may possess biodegradability and thus may find some applications as novel biomaterials.
Conclusions: The thermal properties of the new type of polyamides based on benzene dicarboxylic acid, pyridine dicarboxylic acid, and α-amino acid (alanine and valine) linked to benzidine and 4,4'-oxydianiline were evaluated by thermal gravimetric (TG), differential thermal gravimetric (DTG) and differential thermal analysis (DTA) techniques. Results revealed that the structure-thermal property correlation based on changing the dicarboxylic acid monomer or the diamine monomer demonstrated an interesting connection between a single change (changing the dicarboxylic acids in each series while the diamine is fixed) and thermal properties. In addition, pyridine-containing polymers exhibited semicrystalline characteristic with melting temperature, Tm. where none of the valine-containing polymers showed a melting and crystallization peak indicating that the polymers were amorphous. This is expected since L-valine side chain can inhibit close packing and eliminate crystallization. The newly prepared polymers may possess biodegradability and thus may find some applications as novel biomaterials.

Post-translational arginylation of ornithine decarboxylase from rat hepatocytes

Ornithine decarboxylase (ODC) was purified 6500-fold from NMRI mouse kidneys under conditions designed to inhibit degradation by proteinases. The enzyme was homogeneous by SDS/polyacrylamide-gel electrophoresis, and the specific activity was among the highest reported. The yield was 70%. A monoclonal antibody against this preparation was generated and used in studies to investigate the half-life of ODC in cultured rat hepatocytes labelled with [35S]methionine. This value was 39 +/- 4 min and was unchanged when either NH4Cl (as a lysosomotropic agent) or leupeptin (as a lysosomal proteinase inhibitor) was added to the culture medium. Thus the intracellular turnover of ODC in cultured hepatocytes occurs mainly in extra-lysosomal compartments. Arginylation of rat ODC was investigated in vitro by incubation with L-[3H]arginyl-tRNA, and the incorporation of the label was compared with that of total cytosolic proteins. Arginylated ODC had a specific radioactivity 8600 times that of the bulk of cytosolic protein. Edman degradation of this ODC showed that the post-translational arginylation occurred only at the alpha-amino end of the enzyme. The inhibitor of arginyl-tRNA:protein arginyltransferase (EC 2.3.2.8), L-glutamyl-L-valyl-L-phenylalanine, increased the half-life of ODC in cultured hepatocytes from 39 min to more than 90 min. The possible significance of the preferential post-translational arginylation of ornithine decarboxylase to its rapid turnover is discussed.

Post-translational arginylation and intracellular proteolysis

Cellular proteins may be designated to fast degradation by their N-terminal amino acids, and especially a N-terminal arginine residue should have an extremely destabilizing effect on cytosol proteins. We investigated the post-translational arginylation of cytosol proteins and especially of ornithine decarboxylase (ODC) by the cytosolic enzyme arginyl transferase by incubation with radioactive L-arginyl-tRNA and isolation of ODC with our monoclonal antibody. Arginylated ODC had a specific radioactivity 8600 times that of the bulk of cytosolic proteins and Edman-degradation of this ODC showed that the post-translational arginylation occurred only at the L-amino-end of the enzyme. The inhibitor of arginyltransferase, L-Glutamyl-L-Valyl-L-Phenylalanine, increased the half-life of ODC in cultured hepatocytes from 39 min to more than 90 min. This post-translational arginylation of ODC and also of other cytosol proteins is reversible. At least 25 different cytosol proteins in addition to ODC can be arginylated in hepatocytes, and at least 15 different proteins can be arginylated in Dictyostelium discoideum. The arginylated proteins are much more rapidly degraded by cellular proteinases, especially by calpains, than those cytosolic proteins which are not arginylated.

Isolation and characterization of aminopeptidase (Jc-peptidase) from Japanese cedar pollen (Cryptomeria japonica)

An aminopeptidase, Jc-peptidase, was purified from Japanese cedar pollen by seven steps, including precipitation with ammonium sulfate, ion-exchange chromatography, gel filtration, hydrophobic interaction chromatography on phenyl-agarose, and high-performance liquid chromatography. Purified Jc-peptidease has a molecular weight of 42 kDa and hydrolyzes the synthetic substrates of L-phenylalanyl-4-methylcoumaryl-7-amide (Phe-MCA) with Km = 5 x 10(-5) M, Tyr-MCA with Km = 7 x 10(-4) M, Leu-MCA with Km = 1 x 10(-3) M, and Met-MCA with Km = 1 x 10(-3) M. Other MCA analogues such as Arg-MCA or Glu-MCA failed to serve as its substrates. The activity was inhibited in the presence of phebestin, [(2S,3R)-3-amino-2-hydroxy-4-phenylbutanoyl-L-valyl]-L-phenylalanine, with Ki = 4.7 x 10(-5) M, or bestatin, [(2S,3R)-3-amino-2-hydroxy-4-phenylbutanoyl]-L-leucine, with Ki = 1.1 x 10(-4) M. According to amino acid sequence analysis, the N-terminal amino group seems to be blocked. The physiological function of the aminopeptidase (Jc-peptidase) has not been clarified in vivo.