Deuterium exchange and protein structure 



K. LINDERSTR0M-LANG 



The Carlsberg Laboratory, Copenhagen, Denmark 



1. INTRODUCTION 



In a series of recent papers by Hvidt, Johansen, Vaslow, Berger, and my- 

 seifi.2.3.4.5.6,7,8.9 ^ study was made of the rate of deuterium exchange 

 between ordinary water and proteins or peptides in which all the easily ex- 

 changeable hydrogen atoms, i.e. those bound to oxygen, nitrogen, and sul- 

 phur atoms, had been replaced by deuterium atoms. The conditions under 

 which this rate of exchange was studied were varied within rather wide limits, 

 the temperature e.g. was varied from 0° to 40°C, pH from 2 to 8. In some 

 cases buffer, in others denaturing agents like urea or guanidinium chloride 

 were added. 



The results may be summarized as follows : 



1. Neglecting the possibility that the exchange of one deuterium atom 

 may influence the rate of exchange of another, the rate curve for any peptide 

 or protein may be represented by a sum of first order terms, viz. : 



n„-n-=^me-ß^'; 'Em=n^ (1) 



where n^ is the total number of exchangeable deuterium atoms per peptide 

 or protein molecule and m the number of atoms within any group charac- 

 terized by the same rate constant ßt. The quantity n is the average number 

 of exchanged deuterium atoms at the time t. The half-time of the rate group 

 / is given by 



ln2 0-6932 .^^ 



('.>' 



ßi ßi 



As everybody knows, most kinetic data (and ours too) can be represented 

 by such exponential series and the number of constants ßt required is the 

 smaller, the less accurate the experiments. 



2. The deuterium atoms bound to oxygen and nitrogen in the end groups 

 or side chains of peptides and proteins seem to exchange fast in most cases, 

 viz. with a half-time of less than 0-5 min. at pH 3 and 0", i.e. with a velocity 

 which is too high to be picked up by our methods, a point to be discussed 



