Reaction of dihydropyrrolizines with deoxyribonucleic acids in vitro.

1. Thermal denaturation profiles of Escherichia coli DNA pretreated with monocrotaline pyrrole in vitro showed no difference from control DNA samples during heating. A substantial increase in the degree of renaturation during cooling of the pretreated DNA samples was observed. The degree of renaturation was dependent on the concentration of pyrrole used. 2. When rat liver DNA was pretreated with monocrotaline pyrrole there was a greater degree of renaturation after heat treatment than was found with E. coli DNA. 3. Equilibrium-density-gradient centrifugation in alkaline caesium chloride showed that DNA pretreated with monocrotaline pyrrole and heat denatured, renatured to a greater extent on quenching in ice than did untreated control DNA. The degree of renaturation was similar whether the initial treatment of the DNA with pyrrole was for 1 or for 15min. The reaction also appeared to be independent of pH between 5.5 and 9.0. 4. Retrorsine pyrrole was as effective as monocrotaline pyrrole in cross-linking the DNA, but monocrotaline pyrrole exposed to water for 5min before the addition of the DNA was ineffective. Pretreatment of E. coli DNA with synthetic bis-hydroxymethylpyrrole esters also caused renaturation after heat treatment. Monoesters were ineffective. 5. After treatment of rats with retrorsine, no cross-linking of the liver DNA could be demonstrated.