Use of high concentrations of dimethylnitrosamine in bacterial lethality, mutagenesis, and enzymological studies.

Extreme caution should be exercised when one interprets results of in vitro studies on bacterial lethality, mutagenesis, and dimethylnitrosamine-demethylase activity obtained with dimethylnitrosamine at concentrations of 20 mM or higher. In fact, previous investigations in our laboratory have shown that dimethylnitrosamine as well as other nitrosamines are powerful hydrogen-bonding agents (5) and denaturing agents toward ovalbumin used as a model protein (6, 7, 10). These studies have established that the potency of dimethylnitrosamine and diethylnitrosamine in bringing about conformational changes in protein is com parable to that of urea and guanidinium chloride, wellknown protein-denaturing agents (e.g., Refs. 1, 15, and 19). The optical rotatory dispersion study (10) of the oval bumin conformational change as a function of dimethylni trosamine concentration indicated, moreover, aconcentration-dependent ambivalent effect on protein conformation. Thus, at concentrations of, and greater than, about 200 HIM,dimethylnitrosamine brings about denaturation; this is indicated by the successive decrease of the Moffit-Yang b„ constant (10), a measure of the percent helix content of proteins, as well as by the gradual increase of "reduced"