Interaction between Serratia protease and human plasma alpha 2 macroglobulin.

Serratia protease (TSP) [EC 3.4.24] was bound stoichiometrically to alpha 2 macroglobulin (alpha 2M), which was purified and crystallized from human plasma, but apo TSP was not bound. On formation of the TSP-alpha 2M complex the enzymatic activity of the bound TSP was affected with respect to substrates; Km values of the bound TSP were unchanged but Vmax values were reduced. alpha 2M was cleft at the mid-region of its subunits chains by TSP, which resulted in a conformational change of the alpha 2M molecule with TSP.