Granzyme A (EC 3.4.21.78, CTLA3, HuTPS, T-cell associated protease 1, cytotoxic T lymphocyte serine protease, TSP-1, T-cell derived serine proteinase) is an enzyme. This enzyme catalyses the following chemical reaction Granzyme A (EC 3.4.21.78, CTLA3, HuTPS, T-cell associated protease 1, cytotoxic T lymphocyte serine protease, TSP-1, T-cell derived serine proteinase) is an enzyme. This enzyme catalyses the following chemical reaction This enzyme is present in cytotoxic T lymphocyte granules.