title: The kinetics of conformational changes of alpha 2-macroglobulin determined by time resolved X-ray solution scattering.
abstract: The rate of gross conformational change of alpha 2-macroglobulin (alpha 2M) during its proteinase trapping was directly determined for the first time using time-resolved X-ray solution scattering. Decrease of radius of gyration was observed under pseudo-first-order conditions with excess proteinases, which exhibited a monophasic time-course. The rate constants were 0.5 +/- 0.1 s-1 and 0.8 +/- 0.2 s-1 for the reaction with chymotrypsin and trypsin, respectively. There was no concentration dependence of the observed rate constants. Therefore, the rate-limiting step of the gross conformational change was not the bimolecular encounter reaction between alpha 2M and proteinases, which requires a new proposal of pre-trapping of proteinases before the gross conformational change.
authors.affiliation: Faculty of Bioscience and Biotechnology, Tokyo Institute of Technology, Kanagawa, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Arakawa
authors.forename: T
authors.initials: T
authors.lastname: Urisaka
authors.forename: H
authors.initials: H
authors.lastname: Tsuruta
authors.forename: Y
authors.initials: Y
authors.lastname: Amemiya
authors.forename: H
authors.initials: H
authors.lastname: Kihara
authors.forename: A
authors.initials: A
authors.lastname: Ikai
mesh_terms: D002918:Chymotrypsin; D006801:Humans; D007700:Kinetics; D011487:Protein Conformation; D013997:Time Factors; D014357:Trypsin; D014961:X-Ray Diffraction / Q000379:methods; D000511:alpha-Macroglobulins / Q000737:chemistry*
chemical_list: D000511:alpha-Macroglobulins; D002918:Chymotrypsin; D014357:Trypsin