Kinetic evidence of a distinct regulatory site on 15-hydroxyprostaglandin dehydrogenase

15-Hydroxyprostaglandin dehydrogenase was inhibited by xylocaine, furosemide, and ethacrynic acid, but was activated by imipramine and other related drugs. Inhibition by xylocaine was uncompetitive with respect to both NAD+ and PGE1. Activation by imipramine was also uncompetitive with respect to both substrates. Kinetic studies on mixed inhibitor and activator showed a competitive pattern of inhibition of xylocaine vs imipramine activation. These studies suggest that either inhibitors or activators interact with the enzyme at a site distinct from substrate and coenzyme binding sites, and that inhibitors and activators probably interact with the enzyme at the same regulatory site.