Activity assays of SorPS9 and point mutants. (A) LC/MS analysis of incubations with 1 revealed wild-type SorPS9 generated 2a and/or 2b, while the H33A mutant was inactive. The N186H and N186A mutants showed some activity, but no activity was observed from the N186D mutant. Traces show extracted ion current at m/z 268. (B) LC/MS analysis of incubations with 3a+3b revealed wild-type SorPS9 generated syn-pyran products (4a and/or 4d) and anti-pyran products (4b and/or 4c), while the H33A mutant was inactive. Again, the N186H and N186A mutants showed some activity, but no activity was observed from the N186D mutant. Traces show extracted ion current at m/z 282.