- Cathepsin L in secretory vesicles functions as a prohormone-processing enzyme for production of the enkephalin peptide neurotransmitter. Yasothornsrikul, S., Greenbaum, D., Medzihradszky, K.F., Toneff, T., Bundey, R., Miller, R., Schilling, B., Petermann, I., Dehnert, J., Logvinova, A., Goldsmith, P., Neveu, J.M., Lane, W.S., Gibson, B., Reinheckel, T., Peters, C., Bogyo, M., Hook, V. Proc. Natl. Acad. Sci. U.S.A. (2003)