1. Ab initio conformational study of N-acetyl-L-proline-N',N'-dimethylamide: a model for polyproline
Young Kee Kang, Hae Sook Park Biophys Chem. 2005 Jan 1;113(1):93-101. doi: 10.1016/j.bpc.2004.08.002.
We report here the results on N-acetyl-l-proline-N',N'-dimethylamide (Ac-Pro-NMe2) as a model for polyproline at the HF/6-31+G(d) level with the conductor-like polarizable continuum model of self-consistent reaction field methods to figure out the conformational preference and cis-trans isomerization of polyproline in the gas phase, chloroform, methanol, and water. The second methyl substitution at the carboxyl amide end results in different backbone structures and their populations from those of N-acetyl-L-proline-N-methylamide (Ac-Pro-NHMe). In particular, all conformations with the C7 hydrogen bond between acetyl and amide ends, which is the most probable conformations of Ac-Pro-NHMe in the gas phase and in nonpolar solvents, disappeared for Ac-Pro-NMe2 even in the gas phase due to the lack of amide hydrogen. The dominant conformation for Ac-Pro-NMe2 is the polyproline II structure with the trans prolyl peptide bond in the gas phase and in solutions. In methanol, the population of the polyproline I structure with the cis prolyl peptide bond is calculated to be larger than that in water, which is consistent with experiments. It should be noted that Ac-Pro-NMe2 has higher rotational barriers for the cis-trans isomerization of the Ac-Pro peptide bond than Ac-Pro-NHMe in the gas phase and in solutions, which could be due to the lack of the intramolecular hydrogen bond between prolyl nitrogen and carboxyl N-H group for the transition state of Ac-Pro-NMe2. The rotational barriers for Ac-Pro-NMe2 are increased with the increase of solvent polarity, as seen for Ac-Pro-NHMe.
3. Purification and characterization of a novel aminoacylase from Streptomyces mobaraensis
Mayuko Koreishi, Fumiaki Asayama, Hiroyuki Imanaka, Koreyoshi Imamura, Megumi Kadota, Takuo Tsuno, Kazuhiro Nakanishi Biosci Biotechnol Biochem. 2005 Oct;69(10):1914-22. doi: 10.1271/bbb.69.1914.
A novel aminoacylase was purified to homogeneity from culture broth of Streptomyces mobaraensis, as evidenced by SDS-polyacrylamide gel electrophoresis (PAGE). The enzyme was a monomer with an approximate molecular mass of 100 kDa. The purified enzyme was inhibited by the presence of 1,10-phenanthroline and activated by the addition of Co2+. It was stable at temperatures of up to 60 degrees C for 1 h at pH 7.2. It showed broad substrate specificity to N-acetylated L-amino acids. It catalyzed the hydrolysis of the amide bonds of various N-acetylated L-amino acids, except for Nepsilon-acetyl-L-lysine and N-acetyl-L-proline. Hydrolysis of N-acetyl-L-methionine and N-acetyl-L-histidine followed Michaelis-Menten kinetics with K(m) values of 1.3+/-0.1 mM and 2.7+/-0.1 mM respectively. The enzyme also catalyzed the deacetylation of 7-aminocephalosporanic acid (7-ACA) and cephalosporin C. Moreover, feruloylamino acids and L-lysine derivatives of ferulic acid derivatives were synthesized in an aqueous buffer using the enzyme.