The kinetics of conformational changes of alpha 2-macroglobulin determined by time resolved X-ray solution scattering.
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.
Arakawa
H
H
Faculty of Bioscience and Biotechnology, Tokyo Institute of Technology, Kanagawa, Japan.
Urisaka
T
T
Tsuruta
H
H
Amemiya
Y
Y
Kihara
H
H
Ikai
A
A
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*
D000511:alpha-Macroglobulins; D002918:Chymotrypsin; D014357:Trypsin