Most enzymes do in fact work on a single substrate in most cases, this is because of the enzyme - substrate specificity. Certain reactant molecules acting as substrates can only fit in the "lock" of particular enzymes and undergo a conformational change and result in Unique products to be released after the reaction has occurred.
Answer: If there is too much heat or pressure, the rock will melt and become magma. This will result in the formation of an igneous rock, not a metamorphic rock. Consider how granite changes form. ... When granite is subjected to intense heat and pressure, it changes into a metamorphic rock called gneiss.
Hope this helps....... Stay safe and have a Merry Christmas!!!!!!!!! :D