Quinolactacins, which inhibit tumor necrosis factor production, contain a quinolone skeleton conjugated with a y-lactam. The biosynthesis of quinolactacin was investigated by feeding experiments using 13C single-labeled precursors (sodium [1-13C]acetate, DL-[1-13C]-isoleucine, L-[methyl-13C]methionine, and sodium [1-13C]-anthranilate) and D-[U-13C]glucose.