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.

THE PHOTOASSIMILATION OF SUCCINATE TO HEXOSE BY RHODOSPIRILLUM RUBRUM

1. A pathway for the synthesis of hexose from succinate by Rhodospirillum rubrum is proposed. 2. With 2,3-(14)C(2)-labelled succinate and fumarate as substrates in experiments with chromatophores and a soluble enzyme fraction of R. rubrum it was found that the products of succinate metabolism by the extracts were the same as in whole cells. It was also found that the light-dependent oxidation of succinate was catalysed by the chromatophores, but that all the other enzymes involved were in the soluble fraction. 3. By using specific assays the presence of all the enzymes required for the proposed pathway was demonstrated in the extracts and their specific activities were measured. 4. The overall rate of succinate assimilation was measured manometrically. The activities of the enzymes assayed were sufficient to account for the overall rate of assimilation. It is concluded that the proposed pathway represents the major mechanism for synthesis of hexose from succinate in R. rubrum. 5. The formation of alanine and aspartate was observed in experiments with isotopically labelled substrates, and possible synthetic pathways for these compounds are discussed.

ENZYMES RELEASED FROM ESCHERICHIA COLI WITH THE AID OF A SERVALL CELL FRACTIONATOR

The release and stability of the enzymes S-adenosylhomocysteine nucleosidase, lysine decarboxylase, arginine decarboxylase, glutamic decarboxylase, formic hydrogenlyase, formic oxidase, and glucose oxidase from Escherichia coli during disruption of the organisms in a Servall-Ribi refrigerated cell fractionator were examined. With the possible exception of arginine decarboxylase, maximal activity was retained by all the enzymes reported here when the cell suspensions were processed at pressures necessary for rupture of all the organisms (15,000 to 25,000 psi). Considerable variation in the stability of different enzymes liberated by disruption at higher pressures (45,000 to 55,000 psi) was observed. It is reasonable to assume that mechanical forces rather than effects of temperature are responsible for inactivation of these enzymes.

A RAPID IMMUNOFLUORESCENCE TECHNIQUE FOR DETECTING SALMONELLAE IN RAW MEAT

A rapid 18 hr. technique has been developed for detecting salmonella contaminated carcass and boneless meats. It is based on 43° C. selenite enrichment of samples, followed by immunofluorescent detection of salmonella cells in the enrichment. In tests with 286 meat samples the rapid and conventional techniques agreed in the detection of 93 positive and 149 negative samples. The two tests failed to agree for the remaining 44 samples. The rapid technique thus lacks precision, but could be used as a rapid ‘presumptive’ salmonella test, so that contaminated material could be prevented from reaching the processing lines of food factories.

We thank Dr Betty Hobbs of the Food Hygiene Laboratory for kindly sup plying the meat samples used in this investigation, Dr Patricia Bradstreet of the Standards Laboratory for Serological Reagents for the salmonella diagnostic antisera and Mr R. Kenworthy for performing the goat injections.

NICOTONIC ACID BIOSYNTHESIS: CONTROL BY AN ENZYME THAT COMPETES WITH A SPONTANEOUS REACTION

Extracts of livers from diabetic rats contain normal amounts of the enzymes needed to convert 3-hydroxyanthranilic acid to nicotinic acid nucleotide. The decreased capacity of diabetic animals to synthesize nicotinic acid is therefore attributed to increased amounts of picolinic carboxylase, which competes for a common intermediate with the spontaneous reaction in which quinolinic acid is formed as a precursor of nicotinic acid. These studies were facilitated by the synthesis of 3-hydroxyanthranilic acid labeled with carbon-14 in positions 3 and 6

INDUCTION AND MULTI-SENSITIVE END-PRODUCT REPRESSION IN THE ENZYMIC PATHWAY DEGRADING MANDELATE IN PSEUDOMONAS FLUORESCENS

1. The first five enzymes involved in the degradation of mandelate in Pseudomonas fluorescens have been examined. 2. Induction is not significantly affected by glucose. 3. The first three enzymes form a group inducible by mandelate and repressible by benzoate, catechol and succinate. 4. The possibility that benzoate and catechol act as repressors only after they have been degraded to succinate is unlikely since mutants blocked at suitable points in the pathway have the same repression pattern as the wild type. 5. It is concluded that synthesis of the enzymes is subject to a multi-sensitive repression mechanism that can be independently activated by benzoate or catechol or succinate. 6. In each case the repression can be largely overcome by increasing the concentration of the inducer. 7. The enzymes of the first group are thus controlled by a dual system in which induction by the first substrate is opposed by repression exerted by the end product of the first group and by the products of succeeding groups.