- Substitution of serine for arginine in position 162 of TEM-type beta-lactamases extends the substrate profile of mutant enzymes, TEM-7 and TEM-101, to ceftazidime and aztreonam. Collatz, E., Tran Van Nhieu, G., Billot-Klein, D., Williamson, R., Gutmann, L. Gene (1989)