title: Opposing effects of NaCl on reversibility and thermal stability of halophilic beta-lactamase from a moderate halophile, Chromohalobacter sp. 560.
abstract: Beta-lactamase from a moderately halophilic organism is expected to show salt-dependent stability. Here we examined the temperature-dependence of stability at different salt concentrations using circular dichroism (CD) and enzyme activity. NaCl showed opposing effects on melting temperature and reversibility of the thermal melting. Increasing NaCl concentration greatly increased the melting temperature from, e.g., 41 degrees C in the absence of NaCl to 61 degrees C in 3 M NaCl. Conversely, reversibility decreased from 92% to 0% in the corresponding NaCl solutions. When beta-lactamase was heated at different temperatures and NaCl concentrations, the activity recovery followed the reversibility, not the melting temperature. Heating beta-lactamase at 63 degrees C, slightly above the onset temperature of melting in 2 M NaCl and far above the melting in 0.2 M NaCl, showed a much greater recovery of activity in 0.2 M NaCl than in 2 M NaCl, again consistent with the reversibility of melting.
authors.affiliation: Applied and Molecular Microbiology, Faculty of Agriculture, Kagoshima University, 1-21-24 Korimoto, Kagoshima 890-0065, Japan.
authors.forename: Hiroko
authors.initials: H
authors.lastname: Tokunaga
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Arakawa
authors.forename: Harumi
authors.initials: H
authors.lastname: Fukada
authors.forename: Masao
authors.initials: M
authors.lastname: Tokunaga
mesh_terms: D002942:Circular Dichroism; D004795:Enzyme Stability; D044129:Halomonadaceae / Q000201:enzymology*; D006358:Hot Temperature; D012965:Sodium Chloride / Q000494:pharmacology*; D013816:Thermodynamics; D001618:beta-Lactamases / Q000737:chemistry* / Q000378:metabolism
chemical_list: D012965:Sodium Chloride; D001618:beta-Lactamases