LC-MS-MS analysis of the metabolite A-74528. Triple quadrupole LC-MS multiple reaction monitoring detection of A-74528 in extracts from (A) wild-type Streptomyces. sp SANK 61196, (B) wild-type Streptomyces griseus, (C) Streptomyces lividans K4-114/pKZ11, (D) mutant Streptomyces sp. SANK 61196ΔKS, (E) Streptomyces lividans K4-114/pKZ11, (F) Streptomyces lividans K4-114/pKZ12, (G) Streptomyces lividans K4-114/pKZ13, and (H) Streptomyces lividans K4-114/pKZ14. The peaks shown correspond to a metabolite with a parent ion of 561 (m/z) and a fragment ion of 417 (presumably corresponding to the loss of the lactone moiety of A-74528)