Effects of chlorpromazine on cell wall biosynthesis and incorporation of orotic acid into nucleic acids in Bacillus megaterium

Abstract

The microorganism Bacillus megaterium was used as a model system for the study of the biochemical basis of action of chlorpromazine. At 33 μM, chlorpromazine (10 μg/ml) doubled the generation time of logarithmic phase cultures of B. megaterium. The effect of the drug on the incorporation of labeled precursors for macromolecules was compared at equivalent turbidities. Incorporation of 14C-orotic acid into RNA and DNA was immediately inhibited. In contrast, incorporation of 14C-adenine, 14C-formate and 14C-thymidine into nucleic acids was unaffected, indicating that nucleic acid synthesis was normal despite interference by the drug in the utilization of exogenous orotic acid. Incorporation of 14C- l-lysine was unaffected, but chlorpromazine immediately inhibited the incorporation of 14-C-diaminopimelic acid into cell wall. Uridine nucleotide precursors (colorimetric assay) for glycopeptide polymer of cell wall accumulated promptly upon addition of the drug. Accumulation was dose dependent and reached eight times that of control cells. Other phenothiazines including trifluoperazine (3 μM), promazine (58 μM), promethazine (156 μM) and chlorpromazine sulfoxide (2 mM) also caused significant accumulation of cell wall precursors. Although the mechanism of action is unknown, it appears that chlorpromazine specifically interferes with cell wall synthesis in B. megaterium.