The intracellular cAMP concentration was measured according to the previous method with some modifications [15 (link)]. YEM30 strain treated with different doses of MPD was incubated in RPMI 1640 medium at 37°C. After 12 h incubation, the intracellular cAMP concentration was measured by a cAMP ELISA Kit (Elabscience Biotechnology Co., China).