A young man takes pa in a nutritional research study in Bangalore. After ingesting a very fatty meal, serum samples are taken for research studies at 1 hour and 3 hours. These studies measure the average diameter of the chylomicrons, showing an average chylomicron diameter of 500 nm at 1 hour, which drops to an average diameter of 150nm at 3 hours. Where is the enzyme responsible for this change located?