Detection of dominant enzyme mutants in mice: model studies for mutations in man

After intraperitoneal injection with the mutagens procarbazine hydrochloride (PHCl) or N-ethyl-N-nitrosourea (ENU), male (101/EL X C3H/EL)F1 mice were mated with untreated test-stock females. The offspring were screened for induced mutations that cause alterations of two different enzyme properties. Charge modifications were analysed by separation of liver enzymes by isoelectric focussing on polyacrylamide gels. Banding patterns of six enzyme systems were checked by using the agar contact replica technique and specific activity stainings. No mutant was found in 5278 offspring of the control group. After paternal treatment of spermatogonia, the mutant frequency was one mutant in 5630 offspring (600 mg PHCl per kg body weight), one mutant in 1892 offspring (160 mg/kg ENU), two mutants and two presumed mutants, which died before genetic confirmation, in 4136 offspring (250 mg/kg ENU). No mutant was detected with PHCl and the two ENU doses in the postspermatogonial treatment groups of 469, 1088, and 2020 offspring, respectively. Specific activities of 10 erythrocyte enzymes were measured in the blood with an automatic enzyme analyser. To date, in the spermatogonial treatment group, findings have been: no mutant in 3610 controls, seven mutants in 3509 offspring (80 mg/kg ENU), five mutants in 800 offspring (160 mg/kg ENU) and four mutants in 759 offspring (250 mg/kg ENU). Of these 16 independent mutants, 10 caused reduced enzyme activity and six increased it.