catalysis: acceleration of a chemical reaction induced the presence of material that is chemically unchanged at the end of the reaction
chemical process: (chemistry) any process determined by the atomic and molecular composition and structure of the substances involved
triiodothyronine: thyroid hormone similar to thyroxine but with one less iodine atom per molecule and produced in smaller quantity; exerts the same biological effects as thyroxine but is more potent and briefer