ENZYMES OF THE PYRIMIDINE PATHWAY IN ESCHERICHIA COLI. II. INTRACELLULAR LOCALIZATION AND PROPERTIES OF DIHYDROOROTIC DEHYDROGENASE

Taylor, W. Herman (Portland State College, Portland, Ore.), and Mary L. Taylor. Enzymes of the pyrimidine pathway in Escherichia coli. II. Intracellular localization and properties of dihydroorotic dehydrogenase. J. Bacteriol. 88:105-111. 1964.-Intracellular localization of three enzymes of the pyrimidine pathway in Escherichia coli was studied. Dihydroorotic dehydrogenase was found to be associated with the membrane portion of lysed spheroplasts. Centrifugal fractionation of cell-free extracts showed all the dihydroorotic dehydrogenase activity to be associated with large structures, probably cell wall-membrane fragments. In contrast, all orotidylic decarboxylase activity was found in the cytoplasm in both lysed spheroplasts and cell-free extracts. Aspartate transcarbamylase activity appeared to be particulate in repressed cells, but only 25% was particulate in derepressed cells. Dihydroorotic dehydrogenase was shown to be bound to oxidative particles by oxygen uptake and orotate production from dihydroorotate. A ferricyanide reduction assay, suitable for measuring soluble and particulate enzyme, was devised for dihydroorotic dehydrogenase. Soluble dihydroorotic dehydrogenase was prepared by use of deoxycholate. A 20-fold purification of the enzyme compared to whole-cell activity was achieved by ammonium sulfate fractionation of the deoxycholate-soluble enzyme. Although cytochromes were implicated by cyanide inhibition of aerobic orotate production by particles, the purified enzyme appeared to be separated from the cytochromes, as shown by lack of cyanide inhibition in the ferricyanide assay. The purified soluble enzyme did not react in the aerobic assay previously used by others for assay of this enzyme. In contrast to the degradative dihydroorotic dehydrogenases reported by other workers, the biosynthetic dihydroorotic dehydrogenase of E. coli did not link to pyridine nucleotides.

PURIFICATION AND PROPERTIES OF DIAMINOPIMELATE DECARBOXYLASE FROM ESCHERICHIA COLI

1. Diaminopimelate decarboxylase from a soluble extract of Escherichia coli A.T.C.C. 9637 was purified 200-fold by precipitation of nucleic acids, fractionation with acetone and then with ammonium sulphate, adsorption on calcium phosphate gel and chromatography on DEAE-cellulose or DEAE-Sephadex. 2. The purified enzyme showed only one component in the ultracentrifuge, with a sedimentation coefficient of 5.4s. One major peak and three much smaller peaks were observed on electrophoresis of the enzyme at pH8.9. 3. The mol.wt. of the enzyme was approx. 200000. The catalytic constant was 2000mol. of meso-diaminopimelic acid decomposed/min./mol. of enzyme, at 37 degrees . The relative rates of decarboxylation at 25 degrees , 37 degrees and 45 degrees were 0.17:1.0:1.6. At 37 degrees the Michaelis constant was 1.7mm and the optimum pH was 6.7-6.8. 4. There was an excess of acidic amino acids over basic amino acids in the enzyme, which was bound only on basic cellulose derivatives at pH6.8. 5. The enzyme had an absolute requirement for pyridoxal phosphate as a cofactor; no other derivative of pyridoxine had activity. A thiol compound (of which 2,3-dimercaptopropan-1-ol was the most effective) was also needed as an activator. 6. In the presence of 2,3-dimercaptopropan-1-ol (1mm), heavy-metal ions (Cu(2+), Hg(2+)) did not inhibit the enzyme, but there was inhibition by several amino acids with analogous structures to diaminopimelate, generally at high concentrations relative to the substrate. Penicillamine was inhibitory at relatively low concentrations; its action was prevented by pyridoxal phosphate.

MUTANT OF SALMONELLA TYPHIMURIUM DEFICIENT IN THE CARBON DIOXIDE-FIXING ENZYME PHOSPHOENOLPYRUVIC CARBOXYLASE

Theodore, Theodore S. (University of Pittsburgh, Pittsburgh, Pa.), and Ellis Englesberg. Mutant of Salmonella typhimurium deficient in the carbon dioxide-fixing enzyme phosphoenolpyruvic carboxylase. J. Bacteriol. 88:946-955. 1964.-Resting cells of Salmonella typhimurium wild type (C(+)dg(s)) and the C(-)dg(s) mutant characterized by impaired glucose and glycerol metabolism are able to oxidize Krebs cycle intermediates to the same extent. The wild type oxidized glucose and pyruvate "completely," and the mutant oxidized these substrates at a reduced rate and incompletely, with the accumulation of acetate. Resting cells of the wild type in the presence of NaHCO(3)-C(14) and glucose incorporated 11 times more CO(2) than did similar suspensions of the mutant. Extracts prepared from cells previously grown in a mineral glucose supplemented medium revealed that the mutant was deficient in the CO(2)-fixing enzyme phosphoenolpyruvic carboxylase (PEP carboxylase). This enzyme was found to be present in the wild-type extracts. It catalyzes the formation of oxaloacetate from phosphoenolpyruvate and CO(2) in the presence of Mn(++) or Mg(++). No added nucleotides are required for its activity. Since only low levels of phosphoenolpyruvic carboxykinase activity are present in extracts prepared from both kinds of cells grown in a mineral glucose supplemented medium, and perhaps only trace amounts of the malic enzyme, phosphoenolpyruvic carboxytransphosphorylase, and of the enzyme requiring pyruvate, CO(2), and adenosine triphosphate are present, it was concluded that PEP carboxylase is required for CO(2), fixation in this organism. The loss of this enzyme prevents the growth of the mutant in a mineral-glucose or mineral-glycerol medium, and results in the incomplete oxidation of glucose and pyruvate with the accumulation of acetate. This is the first demonstration of the essential role of this particular enzyme in CO(2) fixation in chemoorganotrophs.

DIAMINOPIMELIC ACID DECARBOXYLASE OF THE AGENT OF MENINGOPNEUMONITIS

Moulder, James W. (University of Chicago, Chicago, Ill.), Dorothy L. Novosel, and Ilse C. Tribby. Diaminopimelic acid decarboxylase of the agent of meningopneumonitis. J. Bacteriol. 85:701-706. 1963.-Evidence is presented for the presence in meningopneumonitis particles and extracts of an enzyme decarboxylating alpha, epsilon-diaminopimelic acid to lysine and for the absence of a corresponding enzyme in the uninfected host. Properties of the enzyme are described and compared with those of bacterial diaminopimelic acid decarboxylases. The significance of these observations with respect to the mode of lysine biosynthesis in the psittacosis group and to its phylogenetic origin is pointed out.