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PubMed1965

EFFECT OF ENZYMES ON THE INTERACTION OF ENTEROVIRUSES WITH LIVING HELA CELLS.

Zajac, Ihor (Hahnemann Medical College, Philadelphia, Pa.), and Richard L. Crowell. Effect of enzymes on the interaction of enteroviruses with living HeLa cells. J. Bacteriol. 89:574-582. 1965.-Eight crude enzyme preparations and two crystalline enzymes were tested for ability to inactivate coxsackie group B and poliovirus receptors on living HeLa cells. Receptor-destroying enzyme, erepsin, lysozyme, collagenase, proteinase, and cobra venom did not alter attachment of coxsackie B3 or poliovirus T1 to cells, whereas elastase prevented attachment of both viruses tested. Treatment of live cells with pancreatin or chymotrypsin rendered cells unable to attach group B coxsackie viruses, whereas cells treated with trypsin failed to attach poliovirus T1. In addition, chymotrypsin was found to release coxsackie B3 and poliovirus T1 from cell surfaces, whereas trypsin was unable to dissociate virus-cell union. These results indicate that cellular receptors for polioviruses differ from those for group B coxsackie-viruses. The finding that 1% solutions of enzymes will inactivate differentially the enteroviral receptors of HeLa cells, without altering cell viability, provides a useful approach for study of enterovirus receptors of live host cells.

Animals↗
PubMed1981

Catabolite repression of different inducible enzymes in Escherichia coli and the effect of cAMP.

Simultaneous induction of two enzymes sensitive to catabolite repression does not lead to an additive decrease of the specific activity of the two. Exogenously added cAMP increases the specific activity of catabolically repressed enzymes, irrespective of whether the enzyme is induced separately or simultaneously with another enzyme. In the presence of 12 different substrates metabolized by inducible enzymes glucose does not bring about catabolite repression. Synthesis of cAMP is identical with that occurring under conditions when glucose brings about catabolite repression.

Cyclic AMP↗
PubMed1964

CONTROL OF ISOCITRATASE FORMATION IN RHIZOPUS NIGRICANS.

Wegener, Warner S. (University of Cincinnati, Cincinnati, Ohio), and Antonio H. Romano. Control of isocitratase formation in Rhizopus nigricans. J. Bacteriol. 87:156-161. 1964.-A fumaric acid-producing strain of Rhizopus nigricans was found to produce a fair level of isocitratase in a casein hydrolysate medium. Glucose repressed enzyme formation. When glucose was utilized during growth, there was a relief of repression, and enzyme synthesis was resumed at a rate equivalent to that found in nonrepressed cells. Zinc stimulated isocitratase formation in glucose-repressed cultures by stimulating growth and glucose utilization, thereby decreasing accumulation of repressor metabolites derived from glucose. The effectiveness of acetate as an inducer was greater on glucose-repressed cells than on nonrepressed cells; cells grown in the presence of glucose formed higher levels of isocitratase when subsequently replaced with an acetate-containing inductive medium than did cells grown without glucose. Moreover, addition of 2 ppm of Zn(++) during the inductive replacement phase resulted in a twofold increase in isocitratase formation. The hypothesis is submitted that Zn(++) exerts its action by stimulating ribonucleic acid (RNA) synthesis, thereby facilitating the formation of a specific RNA during induction. Preliminary evidence implicating Zn(++) in the stimulation of RNA synthesis in this organism is presented.

Acetates↗
PubMed1983

In vivo study of developmental changes in carbamoyl-phosphate synthetase I in rat liver. Repression of the enzyme synthesis immediately after birth.

The regulatory mechanism of the developmental increase of carbamoyl-phosphate synthetase I in fetal and neonatal rat liver was studied in vivo. The appearance and rapid increase of the enzyme in late fetal period were caused by de novo synthesis of the enzyme protein. The amount of the enzyme protein analyzed by SDS-polyacrylamide gel electrophoresis was proportional to the enzyme activity throughout the period of development. No indication was observed for preexisting protein which could be converted into the active protein. A novel system for the in vivo study of carbamoyl-phosphate synthetase I synthesis was developed. Hepatocytes, mechanically dispersed by repeated passage of the tissue through a pipet, incorporated [35S]methionine into the enzyme. Taking advantage of this system, the regulation of the enzyme synthesis was studied. In vivo synthesis of the enzyme was detected at 4 days before birth and rapidly increased until 1 day before birth. However, the enzyme synthesis was markedly repressed after birth, when the amount of carmamoyl-phosphate synthetase I itself reached the adult level. This result was in a clear contrast with the constant level of the translatable mRNA (Raymond, Y. and Shore, G.C. (1981) Biochim. Biophys. Acta 656, 111-119) and suggested that post-transcriptional regulation is important in addition to the level of mRNA for the regulation of the carbamoyl-phosphate synthetase I level.

Aging↗
PubMed1980

Genetic and physiological characterization of Escherichia coli mutants deficient in phosphoenolpyruvate carboxykinase activity.

Mutants doubly deficient in phosphoenolpyruvate carboxykinase (pck) and phosphoenolpyruvate synthetase (pps) were unable to grow with succinate as the sole carbon source. A number of pck mutations isolated from pps strains by penicillin selection mapped at 74 min on the Escherichia coli chromosome, between glpD and aroB. Several of the strains containing these mutations had a protein antigenically related to phosphoenolpyruvate carboxykinase, and therefore, the mutations probably represented mutations in the structural gene for this enzyme. Phosphoenolpyruvate carboxykinase was regulated at the level of transcription by catabolite repression. Enzyme levels also increased in stationary-phase cultures by a mechanism independent of cyclic adenosine monophosphate or the product of the relA gene.

Chromosome Mapping↗
PubMed1987

lac repressor can regulate expression from a hybrid SV40 early promoter containing a lac operator in animal cells.

The E. coli lac operator and repressor were adapted for function in mammalian cells. Plasmids containing an SV40 early region (pSVlacO) or a chloramphenicol acetyl transferase gene (pSVlacOCAT) linked to a hybrid SV40 early promoter bearing a lac operator were tested for function. Identical plasmids lacking an operator (pX-8 and pX-8CAT) were controls. In vitro, early transcription from pSVlacO, but not from pX-8, was inhibited by lac repressor, and repression was overcome by IPTG. Repression of large T synthesis or CAT activity occurred in vivo only when the respective operator-containing plasmid was cotransfected with a plasmid encoding lac repressor, or when the recipient cells stably synthesized lac repressor. IPTG substantially relieved repression in both cases. CAT enzyme repression was paralleled by a decrease in CAT mRNA abundance. Thus regulatory elements of the lac operon function physiologically in mammalian cells.

Acetyltransferases↗
PubMed1965

BETA-GALACTOSIDASE OF STREPTOCOCCUS LACTIS.

Citti, J. E. (Oregon State University, Corvallis), W. E. Sandine, and P. R. Elliker. beta-Galactosidase of Streptococcus lactis. J. Bacteriol. 89:937-942. 1965.-Synthesis of beta-galactosidase by several strains of Streptococcus lactis was induced by lactose. The rate of hydrolysis of o-nitrophenyl-beta-d-galactopyranoside was used to measure enzyme activity. The enzyme of all but one strain was unstable when whole cells were sonic-treated or treated with toluene; the enzyme of one strain of S. lactis was stable to these treatments, which resulted in at least a fivefold increase in activity over that found in whole cells. The optimal assay conditions for toluene-treated cells of this strain involved incubation at 37 C in pH 7.0 sodium phosphate buffer. Lactose was the most effective inducer of enzyme synthesis. Methyl-beta-d-thiogalactopyranoside, isopropyl-beta-d-thiogalactopyranoside, and galactose were also inducers of the enzyme, but were not as effective as lactose. Melibiose, maltose, and calcium lactobionate were poor inducers of enzyme synthesis. Exogenously supplied glucose repressed enzyme synthesis. The means of control of induced beta-galactosidase synthesis in S. lactis was similar to that in Escherichia coli.

Disaccharides↗
PubMed1967

Formation and operation of the histidine-degrading pathway in Pseudomonas aeruginosa.

Histidine ammonia lyase (histidase), urocanase, and the capacity to degrade formiminoglutamate, which are respectively involved in steps I, II, and IV in the catabolism of histidine, were induced during growth of Pseudomonas aeruginosa on histidine or urocanate, and were formed gratuitously in the presence of dihydro-urocanate. Urocanase-deficient bacteria formed enzymes I and IV constitutively; presumably they accumulate enough urocanate from the breakdown of endogenous histidine to induce formation of the pathway. Urocanate did not satisfy the histidine requirement of a histidine auxotroph, indicating that it probably acted as an inducer without being converted to histidine. The results imply that urocanate is the physiological inducer of the histidine-degrading enzymes in P. aeruginosa. Enzymes of the pathway were extremely sensitive to catabolite repression; enzymes I and II, but not IV, were coordinately repressed. Our results suggest a specific involvement of nitrogenous metabolites in the repression. Mutant bacteria with altered sensitivity to repression were obtained. The molecular weight of partially purified histidase was estimated at 210,000 by sucrose gradient centrifugation. Its K(m) for histidine was 2 x 10(-3)m in tris(hydroxymethyl)aminomethane chloride buffer. Sigmoid saturation curves were obtained in pyrophosphate buffer, indicating that the enzyme might have multiple binding sites for histidine. Under certain conditions, histidase appeared to be partially inactive in vivo. These findings suggest that some sort of allosteric interaction involving histidase may play a role in governing the operation of the pathway of histidine catabolism.

Amidohydrolases↗
PubMed1987

Partial purification and some properties of homoserine O-acetyltransferase of a methionine auxotroph of Saccharomyces cerevisiae.

A wild-type strain and six methionine auxotrophs of Saccharomyces cerevisiae were cultured in a synthetic medium supplemented with 0.1 mM L-cysteine or L-methionine and analyzed for the synthesis of homoserine O-acetyltransferase (EC 2.3.1.31). Among them, four mutant strains exhibited enzyme activity in cell extracts. Methionine added to the synthetic medium at concentrations higher than 0.1 mM repressed enzyme synthesis in two of these strains. The enzyme was partially purified (3,500-fold) from an extract of a mutant strain through ammonium sulfate fractionation and chromatography on columns of DEAE-cellulose, Phenyl-Sepharose C1-4B, and Sephadex G-150. The enzyme exhibited optimal pH at 7.5 for activity and at 7.8 for stability. The reaction product was ascertained to be O-acetyl-L-homoserine by confirming that it produced L-homocysteine in an O-acetyl-L-homoserine sulfhydrylase reaction. The Km for L-homoserine was 1.0 mM, and for acetyl coenzyme A it was 0.027 mM. The molecular weight of the enzyme was estimated to be approximately 104,000 by Sephadex G-150 column chromatography and 101,000 by sucrose density gradient centrifugation. The isoelectric point was at pH 4.0. Of the hydroxy amino acids examined, the enzyme showed reactivity only to L-homoserine. Succinyl coenzyme A was not an acyl donor. In the absence of L-homoserine, acetyl coenzyme A was deacylated by the enzyme, with a Km of 0.012 mM. S-Adenosylmethionine and S-adenosylhomocysteine slightly inhibited the enzyme, but methionine had no effect.

Acetyltransferases↗
PubMed1986

Enterotoxin A synthesis in Staphylococcus aureus: inhibition by glycerol and maltose.

Studies indicated that prior growth of Staphylococcus aureus 196E on glycerol or maltose led to cells with repressed ability to produce staphylococcal enterotoxin A (SEA). A PTS- mutant (196E-MA) lacking the phosphoenolpyruvate phosphotransferase system (PTS), derived from strain 196E, showed considerably less repression of SEA synthesis when cells were grown in glycerol or maltose. Since SEA synthesis is not repressed in the PTS- mutant, repression of toxin synthesis by glycerol, maltose or glucose in S. aureus 196E appears to be related to the presence of a functional PTS irrespective of whether the carbohydrate requires the PTS for cell entry. With lactose as an inducer, glucose, glycerol, maltose or 2-deoxyglucose repressed the synthesis of beta-galactosidase in S. aureus 196E. It is postulated that these compounds repress enzyme synthesis by an inducer exclusion mechanism involving phosphorylated sugar intermediates. However, inducer exclusion probably does not explain the mechanism of repression of SEA synthesis by carbohydrates.

Enterotoxins↗
PubMed1973

Derepression of arylsulfatase synthesis in Aerobacter aerogenes by tyramine.

Studies were made on the effect of tyramine on arylsulfatase synthesis in mutants of Aerobacter aerogenes ATCC 9621 deficient in enzymes involved in tyramine degradation. As shown previously, some sulfur compounds, such as inorganic sulfate, repressed enzyme synthesis while others, such as methionine, did not. Tyramine caused derepression of enzyme synthesis, which is repressed by inorganic sulfate. The present work showed that, although tyramine readily derepressed arylsulfatase synthesis, metabolites of tyramine in either the wild-type or mutant strains did not, so that the derepression is due to the particular structure of tyramine. Kinetic studies on the cells indicated that incorporation of sulfur into protein and enzyme synthesis occurred on supply of either a sulfur compound, which did not cause repression, or of tyramine, which caused derepression, irrespective of the type of sulfur compound added, if any.

Carbon Radioisotopes↗