Non-productive activation of the proteinase binding sites of alpha 2-macroglobulin on reaction of the inhibitor with matrix-linked trypsin.

The reaction of alpha 2-macroglobulin with matrix-linked trypsin is accompanied by apparently identical "bait" region cleavage, thioester cleavage and conformational change as the reaction with the soluble enzyme. However, no binding of proteinase occurs, but instead the inhibitor loses its ability to inactivate soluble trypsin. These findings indicate that the proteinase binding sites of alpha 2-macroglobulin are activated in the normal manner but decay before being able to bind the immobilized enzyme. Such non-productive activation of binding sites may occur also in the reactions of alpha 2-macroglobulin with soluble proteinases, thus explaining apparent enzyme inhibitor stoichiometries of less than 2:1 observed in these reactions.