Somewhat, but not via the mechanism you suggest. Much of pectin is a fiber-type material, but there will be some (not a lot) breakdown of that material to monomer-type sugars. When pectinase is used for many juices to extract sugar, the way it works is to break down cellular wall material (pulp), releasing the juice from inside the cells. So you'll get more juice out of the sap/pulp (depending on the type of juice), but not much additional sugar from the breakdown itself.