Reaction of A.17 with alternative substrates. A.17 was incubated for 1 hour at 37°C with 5 mM each of AEBSF (lane 1), 3 (lane 2), or 4 (lane 3), or 100 μM of 5 (lane 4), 6 (lane 5), or 2 (lane 6), or PBS buffer alone (lane 7). All samples were then incubated for 1 hour at 37°C with 100 μM of 1 and analyzed by western blot as in Figure 3A.