1. Reaction of Lactobacillus histidine decarboxylase with L-histidine methyl ester
T A Alston, R H Abeles Biochemistry. 1987 Jun 30;26(13):4082-5. doi: 10.1021/bi00387a051.
L-Histidine methyl ester inactivates histidine decarboxylase in a time-dependent manner. The possibility was considered that an irreversible reaction between enzyme and inhibitor occurs [Recsei, P. A., & Snell, E. E. (1970) Biochemistry 9, 1492-1497]. We have confirmed time-dependent inactivation by histidine methyl ester and have investigated the structure of the enzyme-inhibitor complex. Upon exposure to either 8 M guanidinium chloride or 6% trichloroacetic acid, unchanged histidine methyl ester is recovered. Formation of the complex involves Schiff base formation, most likely with the active site pyruvyl residue [Huynh, Q. K., & Snell, E. E. (1986) J. Biol. Chem. 261, 4389-4394], but does not involve additional irreversible covalent interaction between inhibitor and enzyme. Complex formation is a two-step process involving rapidly reversible formation of a loose complex and essentially irreversible formation of a tight complex. For the formation of the tight complex, Ki = 80 nM and koff = 2.5 X 10(-4) min-1. Time-dependent inhibition was also observed with L-histidine ethyl ester, L-histidinamide, and DL-3-amino-4-(4-imidazolyl)-2-butanone. No inactivation was observed with glycine methyl ester or histamine. We propose that in the catalytic reaction the carboxyl group of the substrate is in a hydrophobic region. The unfavorable interaction between the carboxylate group and the hydrophobic region facilitates decarboxylation [Crosby, J., Stone, R., & Liehard, G. E. (1970) J. Am. Chem. Soc. 92, 2891-2900]. With histidine methyl ester this unfavorable interaction is no longer present; hence, there is tight binding.(ABSTRACT TRUNCATED AT 250 WORDS)
2. Type II' beta-bend conformation of tert.-butyloxycarbonyl-L-amino-succinyl-L-alanyl-glycine methyl ester in the solid state
S Capasso, L Mazzarella, F Sica, A Zagari Int J Pept Protein Res. 1984 Dec;24(6):588-96. doi: 10.1111/j.1399-3011.1984.tb03164.x.
Boc-L-Asu-L-Ala-Gly-OMe crystallizes in the monoclinic space group P2(1) with cell dimensions a = 14.315 (3) A, b = 9.280 (2) A, c = 14.358(3) A, beta = 103.63(1) A, V= 1853.4 (9) A3, with two molecules in the asymmetric unit. The conformation of the two molecules is characterized by a type II' beta-bend, similar to that predicted earlier by potential energy calculations, stabilized by an intramolecular hydrogen bond. I.r. and 1H-n.m.r. data show that the folded conformation is also stable in chloroform solution.
