Poly(3-hydroxybutyrate)-depolymerase from Pseudomonas lemoignei: catalysis of esterifications in organic media

Lipase catalysis in nonaqueous media is recognized as a powerful tool in organic and more recently polymer synthesis. Even though none of the currently known polyhydroxyalkanoate (PHA) depolymerases have lipase activity, they do have a catalytic center that resembles that of lipases. Motivated by the above, the potential of using the poly(3-hydroxybutyrate), PHB, depolymerase from Psuedomonas lemoignei in organic media to catalyze ester-forming reactions was investigated. The effect of different organic solvents (benzene-d(6), cyclohexane-d(12), and acetonitrile-d(3)) on the activity of the PHB-depolymerase toward propylation of L-lactide was studied. A significant difference in the catalytic rate was observed as a function of solvent polarity. The selectivity of the PHB-depolymerase (P. lemoignei) to catalyze the propylation of a series of different lactones including epsilon-caprolactone, delta-butyrolactone, gamma-butyrolactone, and D, L, meso, and racemic lactides has been studied with the PHB-depolymerase (P. lemoignei) in organic solvents. Important differences in the reactivity of these lactones, as well as selective hydrolysis of stereochemically different linear lactic acid dimers, were observed. Moreover, the ability of the PHB-depolymerase to catalyze the solventless polymerization of epsilon-caprolactone and trimethylene carbonate was investigated.     

Location of alkali metal binding sites in endothelin A selective receptor antagonists, cyclo(D-Trp-D-Asp-Pro-D-Val-Leu) and cyclo(D-Trp-D-Asp-Pro-D-Ile-Leu), from multistep collisionally activated decompositions

We previously showed by using mass spectrometry that endothelin A selective receptor antagonists BQ123 and JKC301 form novel coordination compounds with sodium ions. This property may underlie the ability of an ET(A) antagonist to induce net tubular sodium reabsorption in the proximal tubule cells and reverse acute renal failure induced by severe ischemia. We have now defined the metal binding sites on BQ123 and JKC301 by subjecting the metal-containing peptides to multiple stages of collisionally activated decomposition (CAD) in an ion trap mass spectrometer. When submitted to low-energy CAD, the ring opens at the Asp-Pro amide bond. The metal ion, which bonds, inter alia, to the carbonyl oxygen of the proline residue, acts as a fixed charge site, and directs a charge-remote, sequence-specific fragmentation of the ring-opened peptide. Amino acid residues are sequentially cleaved from the C-terminal end, and the terminal aziridinone structure moves one step toward the N-terminus with each C-terminal amino acid residue removed. These observations are the basis of a new method to sequence cyclic peptides. Amino acid residues are observed as sets of three ions, a*(n)PD, b*(n)PD and c*(n)PD where n is the number of amino acid residues in the peptide.     

JASMS starts its tenth year

Editorial

JASMS starts its tenth year     

Quantitative infrarotspektroskopische Analyse von Styrol-Acrylnitril-Copolymeren nach pyrolytischer Zersetzung

Ohne Zusammenfassung

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Quantitative infrared-speotroscopic analysis of styrene-acrylonitrile copolymers after pyrolytic decomposition

     

Charge transfer prior to fusion

Zeitschrift für Physik A Hadrons and nuclei - In reactions between very asymmetric projectile-target systems charge is preferably transferred from the lighter to the heavier nucleus. This...     

Nuclear size dependence of inclusive particle production

The inclusive production of π⁺, π^?, K⁺, K^?, p and $\text{p}$ for protons incident on carbon and tungsten targets was studied at the Internal Target Area of the Fermilab. We assume an A^α dependence for the inclusive cross sections and report here on the variation of α with incident momentum, transverse momentum and particle species.     

Ion cyclotron resonance spectrometry. A means of evaluating ‘kinetic shifts’

Ion Cyclotron Resonance Spectrometry Is Proposed As The Method For Evaluating ‘Kinetic Shifts.’ The Proposal Is Tested By A Comparison Of The Appearance Potentials For Some Simple Cleavage Reactions With Those For Some Cleavage And Rearrangement Fragmentations In Benzene, Benzonitrile, Anisole, Aniline And Cubane.