Mucochloric acid action on phi X174 DNA: a comparison to other chlorine-substituted 2(5H)-furanones

The action of the drinking water mutagen 3,4-dichloro-5-hydroxy-2(5H)-furanone (MCA) on the plasmid phi X174 converted this initially closed circular, supercoiled (SC) DNA to its relaxed (R) and linear (L) forms. Kinetic analysis of this process gave results coinciding with a sequential, two-step cleavage model whereby the SC was cleaved to the R form, which in its turn was cleaved to the L form. The actions of two additional chlorine-substituted 2(5H)-furanones, reduced MCA (RMCA) and the C-5 isopropyl ether of MCA (MCA-IPE), were compared to that of MCA. Incubation of SC-phi X174 with RMCA gave R form only while MCA-IPE had virtually no effect. Likewise, neither methyl methanesulfonate nor sodium azide cleaved SC-phi X174 to its L form, under conditions whereby MCA caused the formation of L form. Also, 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX) caused formation of R form, but no apparent L form. Increasing concentration of glutathione diminished cleavage of SC phi X174 by MCA, but increased cleavage for MX. The DNA cleavage action of MCA was unique, among the several stronger and weaker mutagens investigated, in its action phi X174.