Explain the activity of protease at pH 4.0 and at pH 7.0.

1 pH 4 is the optimum (pH) ; 2 pH 7 enzyme is denatured ; 3 enzyme / protein / active site, has changed shape at pH 7; 4 shape of active site is complementary to substrate (4) / not (7) ; 5 enzyme-substrate complexes form (4) / not (7) ; 6 (most) effective collisions (between enzyme and substrate) (4) / none (7) ;