Hydrogen‐Deuterium Exchange of Subtilisin Type Carlsberg and Subtilisin Type Novo

The hydrogen‐deuterium exchange of diisopropyl phosphate‐inhibited subtilisin (DIP‐subtilisin) Carlsberg type and DIP‐subtilisin Novo type has been measured in the pD interval 2–8. In the pD range 4.5–8 the native DIP‐subtilisins demonstrated closely related exchange properties, especially with respect to the more slowly exchanging fractions of the peptide hydrogens, and this is taken as support for the hypothesis that the two subtilisin molecules have the same internal folding of the peptide chains. The subtilisins exhibit slower exchange rates than any other proteins thus far investigated. The acid denaturation of subtilisin Carlsberg from pD 2–4 is accompanied by the formation of β‐structure. A similar transformation was not observed with subtilisin Novo.