Regioselective modification of Lysine's amino groups by proteases.

The regioselectivity of six serine proteases for the amino groups of lysine was investigated. alpha-Chymotrypsin showed a preference for the alpha-amino group, although the selectivity can be varied 10-fold depending on the reaction medium. Subtilisin Carlsberg and other bacterial proteases were highly specific for the epsilon-amino group, regardless of the reaction medium: they were used as catalysts for the preparative synthesis of isopeptides in anhydrous tert-amyl alcohol.