The inhibition by nitrate of enzyme formation during growth of Escherichia coli.

During an investigation of the effects of nutrients on formic hydrogenlyase activity in Escherichia coli, it was noted that the harvested cells possessed no measurable formic hydrogenlyase activity when grown in a basal medium composed of inorganic salts and glucose and containing NH4NOs as the sole source of nitrogen. This was in agreement with the data reported in a previous communication (Billen and Lichstein, 1951). Addition of tryptone to the basal medium contaning the NH4NO3 did not cause an expected increase in formic hydrogenlyase activity; however, when (NH4)2HP04 was substituted for NH4NO3 in the tryptone containing basal medium, the harvested cells contained formic hydrogenlyase activity. Since ammonium ions were present in both media and the phosphate concentrations were approximately the same, a nitrate inhibition of formic hydrogenlyase formation was suggested. A review of the literature revealed several other observations of this nature. Pakes and Jollyman (1901) observed that during growth of E. coli in medium containing nitrate and formate no hydrogen was evolved, whereas gas formation was noted from cultures grown in the absence of nitrate. These authors assumed that this difference was due to the utilization of the hydrogen in the reduction of nitrate when present. Yudkin (1932) used resting cells to study hydrogen pro-, duction from formate and from glucose and observed that the addition of nitrate to the broth medium in which the cells were grown inhibited the "production of the enzymes" responsible for the hydrogen evolution. Lee and Wilson (1943) noted that the presence of ammonium or nitrate ions in the culture medium caused a reduced hydrogenase activity in Azotobacter and the reduction paralleled a decrease in nitrogen fixation activity. It has been observed (Billen and Lichstein, 1951) that formation of formic hydrogenlyase and hydrogenase requires the presence of certain amino acids during cell multiplication. With this information in mind, the present study was undertaken with the hope of elucidating the mechanism of nitrate inhibition of formic hydrogenlyase, hydrogenase, and formic dehydrogenase formation.