ENZYMES OF THE PYRIMIDINE PATHWAY IN ESCHERICHIA COLI I

Taylor, W. Herman (Portland State College, Portland, Ore.), and G. David Novelli . Enzymes of the pyrimidine pathway in Escherichia coli . I. Synthesis by cells and spheroplasts. J. Bacteriol. 88: 99–104. 1964.—Upon release from repression, cells and spheroplasts of two mutants of Escherichia coli efficiently synthesized aspartate transcarbamylase and ornithine transcarbamylase, whereas only cells synthesized dihydroorotic dehydrogenase. Ethylenediaminetetraacetate treatment and sucrose incubation of cells were found to be responsible for the loss of dihydroorotic dehydrogenase synthesis. Spheroplasts required the addition of amino acids and an energy source for the synthesis of aspartate transcarbamylase. Uracil repressed synthesis of aspartate transcarbamylase in spheroplasts as well as in cells. Chloramphenicol inhibition and amino acid requirement for increased aspartate transcarbamylase activity in spheroplasts indicated de novo protein synthesis. E. coli 15, R185-482, and E. coli K-12, 496, were used to study the effect of carbon source and stimulation by orotate and dihydroorotate on synthesis of dihydroorotic dehydrogenase. Only E. coli 15, R185-482, showed any stimulation of dihydroorotic dehydrogenase synthesis. When glucose was the carbon source, orotate but not dihydroorotate stimulated; with glycerol as carbon source, dihydroorotate stimulated and orotate acted as a repressor. These results are discussed in terms of induction and pyrimidine supply to the cells.