title: Urea induced inactivation and unfolding of arginine kinase from the sea cucumber Stichopus japonicus.
abstract: Urea titration was used to study the inactivation and unfolding equilibrium of arginine kinase (AK) from the sea cucumber Stichopus japonicus. Both fluorescence spectral and circular dichroism spectral data indicated that an unfolding intermediate of AK existed in the presence of 1.0 to 2.0 M urea. This was further supported by the results of size exclusion chromatography. The spectral data suggested that this unfolding intermediate shared many structural characteristics with the native form of AK including its secondary structure, tertiary structure, as well as its quaternary structure. Furthermore, according to the residual activity curve, this unfolding intermediate form still retained its catalytic function although its activity was lower than that of native AK. Taken together, the results of our study give direct evidence that an intermediate with partial activity exists in unfolding equilibrium states of AK during titration with urea.
authors.affiliation: Department of Biological Science and Biotechnology, Tsinghua University, Beijing, 100084, China. wangxic@mail.tsinghua.edu.cn
authors.forename: Shu-Yuan
authors.initials: SY
authors.lastname: Guo
authors.forename: Zhi
authors.initials: Z
authors.lastname: Guo
authors.forename: Bao-Yu
authors.initials: BY
authors.lastname: Chen
authors.forename: Qin
authors.initials: Q
authors.lastname: Guo
authors.forename: Shao-Wei
authors.initials: SW
authors.lastname: Ni
authors.forename: Xi-Cheng
authors.initials: XC
authors.lastname: Wang
mesh_terms: D000818:Animals; D001122:Arginine Kinase / Q000737:chemistry* / Q000302:isolation & purification; D004789:Enzyme Activation / Q000187:drug effects; D011489:Protein Denaturation / Q000187:drug effects; D017510:Protein Folding; D011994:Recombinant Proteins / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification; D012616:Sea Cucumbers / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics; D013050:Spectrometry, Fluorescence; D013329:Structure-Activity Relationship; D014508:Urea / Q000494:pharmacology*
chemical_list: D011994:Recombinant Proteins; D014508:Urea; D001122:Arginine Kinase