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E V Porter

Publications and source records attributed to E V Porter.

10 recordsLinked to original sources
PubMed1988

Nucleotide sequence of the beta-D-phosphogalactoside galactohydrolase gene of Lactobacillus casei: comparison to analogous pbg genes of other gram-positive organisms.

Lactose metabolism in Lactobacillus casei occurs via phosphoenolpyruvate-dependent phosphotransferase uptake of lactose and subsequent cleavage of lactose-6-phosphate by beta-D-phosphogalactoside galactohydrolase (P-beta Gal). The genes for lactose uptake and P-beta Gal have been shown to be plasmid-associated in L. casei 64H [Chassy et al., Curr. Microbiol. 1 (1978) 141-144]. The cloned P-beta Gal-coding gene (pbg) previously described [Lee et al., J. Bacteriol. 152 (1982) 1138-1146] was subcloned on a 2.9-kb KpnI-Bg/II fragment isolated from pLZ605. Sequence analysis of this fragment revealed an open reading frame of 1422 bp capable of coding for a protein product containing 474 amino acids and having an Mr of 53,989. The L. casei protein showed a high degree of homology to the proteins whose sequence was deduced from the nucleotide sequence of the pbg genes of Staphylococcus aureus and Streptococcus lactis. Because of the significant homologies observed, as reflected in amino acid content as well as predicted structural characteristics of the three proteins, we suggest a common origin for the P-beta Gals of these three organisms.

Amino Acid Sequence↗
PubMed1982

Purification and kinetic characterization of a specific glucokinase from Streptococcus mutans OMZ70 cells.

Glucokinase (ATP-D-glucose 6-phosphotransferase, EC 2.7.1.2) was purified 144-fold from extracts of sucrose-grown Streptococcus mutans OMZ70 (ATCC 33535) cells. Twenty compounds were tested as potential substrates; only glucose (Km = 0.61 mM) was phosphorylated. The reaction catalyzed by the purified enzyme was dependent on the presence of glucose, nucleoside triphosphate and metal ion; glucose 6-phosphate and ADP were the products. Of the seven nucleoside triphosphates tested, ATP (Km = 0.21 mM) was the most efficient phosphate donor in the enzyme-catalyzed formation of glucose 6-phosphate. Both Mn2+ (relative activity, 173%) and Co2+ (264%) were more efficient than Mg2+ (100%) in supporting the enzyme reaction. The enzyme exhibited a broad maximal activity in the pH range from 7.5 to 9.5. The apparent molecular weight of glucokinase, as determined by gel filtration, was 41 000. With glucose held constant at either saturating or subsaturating levels, ADP was a noncompetitive inhibitor of ATP (Ki = 0.67 mM). ADP was an uncompetitive inhibitor of glucose (Ki = 0.71 mM) when ATP was held constant at either a saturating or subsaturating concentration. Glucose 6-phosphate was a competitive inhibitor of glucose (Ki = 0.31 mM) at saturating ATP and exhibited noncompetitive or mixed inhibition at a subsaturating ATP concentration. Glucose 6-phosphate was not an inhibitor toward ATP at saturating glucose concentrations, but exhibited noncompetitive inhibition at subsaturating glucose concentrations. The kinetic data support the postulation of a sequential mechanism for the glucokinase reaction; they are consistent with an ordered mechanism in which glucose binds first and glucose 6-phosphate dissociates last. Furthermore, the data suggest the existence of more than one enzyme binding site for the substrates of the glucokinase reaction.

Glucokinase↗
PubMed1980

Partial purification and properties of a specific glucokinase from Streptococcus mutans SL-1.

The presence of glucokinase (ATP:D-glucose 6-phosphotransferase, EC 2.7.1.2) activity in seven strains of oral streptococci is demonstrated. The glucokinase purified from Streptococcus mutans SL-1 cells is shown to be a highly specific enzyme, phosphorylating only glucose (eight sugars tested). The enzyme is a true glucokinase: formation of the product, shown here to be glucose 6-phosphate, is dependent on the presence of glucose, ATP, divalent metal ion and enzyme. The Km for glucose is 1.40 mM, the pH optimum for the enzyme is a broad plateu from pH 7.1 to 9.5 and the molecular weight is estimated to be 40 000. The finding of a glucokinase in oral streptococci indicates the existence of an intracellular mechanism of glucose phosphorylation. The implications of this observation are discussed.

Glucokinase↗
PubMed1980

Partial purification and properties of a mannofructokinase from Streptococcus mutans SL-1.

Fructokinase activity was demonstrated in seven strains of oral streptococci. The enzyme purified from Streptococcus mutans SL-1 was capable of phosphorylating both D-fructose and D-mmannose to their respective 6-phosphates. Phosphorylation of both fructose and mannose was dependent on adenosine 5'-triphosphate and a divalent metal ion. The molecular weight of the purified enzyme was estimated to be 49,000. The apparent Km of the enzyme for fructose was 0.63 mM. This enzyme also utilized mannose as a substrate, with an apparent Km for mannose of 0.37 mM. Since the activities of the enzyme toward mannose and fructose were not separated upon purification of the enzyme and since mannose was a competitive inhibitor of fructose phosphorylation, the purified kinase is a single enzyme, mannofructokinase, with dual specificity for both mannose and fructose. A role for this enzyme in carbohydrate metabolism in S. mutans is postulated.

Adenosine Triphosphate↗
PubMed1976

Occurrence and distribution of sucrose-metabolizing enzymes in oral streptococci.

Specific growth rates, growth yields, and the level and cellular distribution of three sucrose-metabolizing enzyme activities were determined for seven oral streptococci (Streptococcus mutans strains E49, BHT, 10449, SL-1, and LM-7, S. sanguis 10558, and S. salivarius 25975). Cultures were grown in a fermentor at pH 6 with either 20 mM glucose or 10 mM sucrose. Generation times varied between 21 and 70 min. Whereas some strains grew 10 to 50% more slowly with sucrose than with glucose, others did not. Growth was always logarithmic, and the growth yields were similar. Glcosyl transferase (EC 2.4.1.5) was largely extracellular; in sucrose cultures it was appreciably lower, but no major shift to a cell-associated form was found. In glucose cultures, the activity varied between 4 and 140 IU per 6-liter culture. The glucan formed was mostly or exclusively water insoluble. Glcosyl transferase was stimulated weakly (60% or less) by various dextrans. Fructosyl transferase (EC 2.4.1.10) was primarily extracellular (except in glucose cultures of S. salivarius) and varied between 0 and 337 IU/culture. In S. salivarius, the extracellular fructosyl transferase was induced by sucrose. In all S. Mutans cultures, the total fructosyl transferase activity was lower after growth with sucrose. All strains had extra- and intracellular invertase (EC 3.2.1.26) activity. Total levels varied between 210 and 3,500 IU/culture. Less extracellular activity was present in sucrose cultures. Only S. salivarius had appreciable activity in the cellular particulate fraction. Invertase activity was significantly higher than the combined glucosyl and fructosyl transferase activities in all cultures.

Fructose↗