RELATIONSHIP BETWEEN ACCESSIBILITY AND REACTIVITY OF LYS, MET AND TYRIN SUBTILISINS DY AND CARLSBERG

The chemical reactivities of lysyl, tyrosyl and methionyl residues in subtilisin DY are compared with the computed accessibilities to the wa ter molecules of the corresponding sensitive atoms in the crystal stru cture of subtilisin Carlsberg. A good correlation between accessibilit ies and reactivity was established for the nonionized specific reagent s glyceraldehyde and chloramine T used for modification of lysine and methionine residues, respectively. In a few cases an apparent deviatio n from the general relationship was established. The disagreement may indicate that differences between crystal and solution structures exis t with altered accessibilities of the atoms under consideration. Howev er, when an electrically charged system takes part in the reaction and it is in low concentration, as in the case of tetranitromethane treat ment where the phenoxylate anion reacts, the correlation is more compl ex. In this case not only the accessibility, but also the electrostati c field around the reacting group, should be taken into account for th e explanation of the reaction observed.