Microbial degradation of nitrosamines. II. Effect of the conditions of growth and enzymic reaction on the nitrosamine breakdown.

The affect of growth conditions of Rhizopus oryzae and eyzymic reaction conditions in the cell-free extract on the degradation of NDMA and NDPA has been investigated. Of the growth conditions, the degradation activities in the growing cells were highest when the strains incubated for one day were inoculated into the popato-malt medium of pH 8.0 containing either NDMA or NDPA. Optimal temperature and nitrosamine concentration for the NDMA degradation were defferent from those for the NDPA degradation, i. e., for both NDMA and NDPA degradation they were 0.03-0.12 and 0.1 mM respectively; while those for the nitrosamine degradation were 20°C and 30°C respectively. No marked difference was found in the activities of the stationary and shaking cultures. The cell-free extract of 3 and 4 days growing-cells which were precultured nuder the optimal conditions obtained were maximally active in degrading NDPA and NDMA respectively. Of the enzymic reaction conditions, the degradation activities in the cell-free extract were highest at temperature 30°C and pH 8.0 under anaerobic condition. The nitrosamine degradation was shown to exhibit a concentration dependence different from the relation found in the growth conditions. Namely, the degradation activities were high in the concentration of more than 0.1 mM.