Kinetic studies of mutation induction by epoxides in Neurospora crassa

Summary

• 1. The macroconidial strain K 3/17 ad-3 A (38701) was used in reverse mutation experiments comparing the mutagenic properties of the epoxides diepoxybutane (DEB) and ethyleneoxide (EO). A microconidial strain with the same ad allele was also used.

• 2. The kinetics of mutation induction for both the monofuctional compound EO and the difunctional compound DEB follows the same generalized equation:

  $$ad^ + \times 10^{ - 6} survivors = a\left( {ct} \right)^b $$

  where a and b are constants for a given epoxide, when the strain and the experimental conditions are defined. The product (ct) is defined as the “dose”, where c and t are the molar concentration of the mutagen and the duration of the treatment, respectively.

• 3. The mutagenic response for a given mutagen is independent of the dose rate, except where the treatment is for an extended duration (t very large), in which case the effect is diminished.

• 4. EO is about 20 times more “effective” than DEB when comparison of mutation frequencies is based on equal doses. The two compounds are equally “efficient”, when mutation frequencies are compared at equal survivals.

• 5. The significance of the kinetic data is considered in relation to some possible models of mutation mechanism. The results are discussed in relation to previous data with this system, and to work by other authors.