Hydrogen-deuterium exchange of bovine plasma albumin

An improved method for studying hydrogendeuterium exchange of proteins dissolved in D₂O has been developed. Certain errors inherent in the original Linderstrøm-Lang method have been minimized and some of the experimental techniques made simpler by use of quantitative infrared analysis for the determination of small amounts of D₂O in H₂O. The method has been applied to a study of the N-F isomerization of bovine plasma albumin. Exchange curves have been obtained in the pD region 2.6-5.9. Analysis of the results leads to a picture of the N-F isomerization in which both N and F forms have two regions of slowly exchanging hydrogens. When isomerization of an N form occurs, the more rapidly exchanging region grows at the expense of the more slowly exchanging region. From the pD dependence of the exchange kinetics it can be concluded that the rates of exchange in the isomerization region are determined by the rates of transconformational openings of protein structure. These results support the microheterogeneity model of Foster et al. (1965) (Foster, J. F., Sogami, M., Peterson, H. A., and Leonard, W. J. (1965), J. Biol. Chem. 240, 2495).