In some recipes for apple and cherry pie, it is suggested to pre-cook the filling at low temperature in order to make pectin heat resistant and so preserve the shape and structure of the fruit. This is explained in McGee's "On Food and Cooking" at page 283 as:
Firm-able vegetables and fruits have an enzyme in their cell walls that becomes activated at around 120F/ 50C (and inactivated above 160F/70C), and alters the cell-wall pectins so that they’re more easily cross-linked by calcium ions
Now my question is, what is this enzyme? Is this enzyme available for purchase? And if so, if I were to add it to a, say, strawberry pie filling, would it help maintain its structure?