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PubMed1962

Blood pyruvate concentration measured by a specific method in control subjects.

A specific method of estimating pyruvate, depending upon the oxidation of reduced nicotinamide-adenine dinucleotide in the presence of lactic dehydrogenase, has been modified to improve its accuracy. The precision of the modification, measured by duplicate analysis, was represented by a standard deviation of 0.03 mg./100 ml. The mean recovery of added pyruvate was 99%. The mean blood pyruvate concentration in 30 fasted subjects, who had no illness known to affect pyruvate metabolism, was 0.44 mg./100 ml. (S.D. 0.05). Blood pyruvate levels were measured at 30-minute intervals for two hours after oral or intravenous administration of glucose. The highest levels obtained in each case were about 0.4 mg./100 ml. higher than the initial level, and were found 60 to 90 minutes after oral administration and 30 to 60 minutes after intravenous administration.

Fasting↗
PubMed1982

Adaptive changes of pyruvate oxidation in perfused heart during adrenergic stimulation.

Pyruvate oxidation was studied in isolated guinea pig hearts perfused under various conditions of work and stimulated by norepinephrine. Hearts metabolized pyruvate alone or in combination with 3-hydroxybutyrate or acetate as substrate. [1-14C]-pyruvate-dependent 14CO2 release into the venous effluent (MVpyr) was, like myocardial oxygen consumption (MVO2), directly related to aortic pressure or filling pressure. At high aortic pressures, ventricular pressure development and not work performance was the major determinant of MVO2 and thus MVpyr. With 1 mM pyruvate as sole substrate, 0.08 microM norepinephrine produced parallel changes in hemodynamic performance, MVO2. MVpyr, and pyruvate dehydrogenase complex (PDC) activity (active form). Similar and dose-dependent effects of norepinephrine were observed during infusion of 5 mM DL-3-hydroxybutyrate as cosubstrate. When 1 mM acetate was applied, MVpyr was also dependent on work performance and norepinephrine stimulation. However, in perfusions with 25 mM potassium chloride, norepinephrine did not enhance hemodynamic function or MVO2 and hence PDC activity and MVpyr. Thus regulation of the PDC in catecholamine-stimulated heart appears to be linked predominantly to myocardial energy demand even when alternative energy-providing substrates are utilized.

Animals↗
PubMedDate not supplied

[Effect of thiamine phosphates on the activity of regulatory enzymes of the pyruvate dehydrogenase complex].

The effect of thiamine triphosphate (ThTP) and thiamine diphosphate (ThDP) on the activity of rat liver pyruvate dehydrogenase complex regulatory enzymes (kinase and phosphatase) was studied in experiments with isolated enzyme preparations. It is shown that ThDP caused a pronounced activation of pyruvate dehydrogenase phosphatase (Ka is equal to 65.0 nM). ThTP inhibits phosphatase competitively against the substrate--the phosphorylated pyruvate dehydrogenase complex. The both thiamine phosphates inhibit the pyruvate dehydrogenase kinase activity almost similarly in concentrations exceeding 10 microM. The physiological significance of the antagonistic action of ThDP and ThTP on the pyruvate dehydrogenase phosphatase activity is discussed.

Animals↗
PubMed1978

[Pyruvate-dehydrogenase deficiency. Lethal course of the disease during infancy (author's transl)].

The course of pyruvate dehydrogenase deficiency in an infant is described. During pregnancy fetal movements were reduced, and since birth severe neurologic involvement was noticed. Permanent metabolic acidosis due to lactic acidemia as well as hyperpyruvic acidemia and hyperalaninemia were present. Alanine accumulated in CSF and urine, urinary excretion of lactate and pyruvate was highly elevated. Pyruvate dehydrogenase activity in a liver biopsy was only 5% of that for normal controls, and pyruvate decarboxylation by cultured fibroblasts was equally decreased. Therapy required permanent administration of bicarbonate. The administration of thiamine had no effect. The infant died within three months. Recently prenatal diagnosis during a subsequent pregnancy of the mother revealed normal results when pyruvate degradation with cultured amniotic fluid cells was investigated, and a healthy child was born.

Acidosis↗
PubMedDate not supplied

[Features of pyruvate and lactate metabolism in tumor-bearing rats following citrate administration].

Everyday administration of citrate (250 mg/kg of body mass) into healthy rats within 4 days inhibited activities of pyruvate kinase, pyruvate dehydrogenase, alanine transaminase and of reverse lactate dehydrogenase in liver tissue but not in sceletal muscles. Within the longer period of citrate administration (8 or 12 days) activities of pyruvate dehydrogenase and alanine transaminase continued to decrease in liver tissue, at the same time, content of pyruvate proceeded to increase in sceletal muscles. More distinct inhibitory effect of citrate on the pyruvate dehydrogenase activity was observed not only in liver tissue but and in sceletal muscles of tumor-bearing animals. Alanine transaminase, which was inactivated in liver tissue of healthy animals after citrate treatment, was markedly activated in tumor-bearing rats in the same conditions. The data obtained suggest that some regulatory functions of citrate were qualitatively transformed in tumor-bearing animals, mainly, in relation to turnover of glucogenic amino acids.

Alanine Transaminase↗
PubMed1993

Identity of D-3-aminoisobutyrate-pyruvate aminotransferase with alanine-glyoxylate aminotransferase 2.

D-3-Aminoisobutyrate-pyruvate aminotransferase (EC 2.6.1.40) and alanine-glyoxylate aminotransferase 2 (EC 2.6.1.44) were co-purified from rat liver as a single protein. The ratio of the two activities remained constant after Sephacryl S-200 chromatography and chromatofocussing. The Km value for beta-alanine as a substrate with 1 mM glyloxylate as amino group acceptor was 1.4 mM. The activity was inhibited by (S)-alanine with Ki = 2.2 mM. The Km for (S)-alanine as substrate with 1 mM glyoxylate as amino group was 6 mM. This activity was inhibited competitively by beta-alanine with Ki = 0.7 mM. (R)-3-aminoisobutyric acid, 5-aminolevulinic acid, NG,NG'-dimethyl-(S)-arginine, and (S)-2-aminobutyric acid were active competitively with respect to beta-alanine with Km of 0.12 mM, 2.1 mM, 6.4 mM and 11.3 mM, respectively. Antiserum to rat liver D-3-aminoisobutyrate-pyruvate aminotransferase inhibited alanine-glyoxylate aminotransferase activity in rat liver in the same way as that of D-3-aminoisobutyrate-pyruvate aminotransferase. Alanine-glyoxylate aminotransferase activity and D-3-aminoisobutyrate-pyruvate aminotransferase activities were inactivated competitively with respect to beta-alanine by 5-fluorouracil and 6-azauracil, which are chemotherapeutic reagents used to cancer. These experiments indicate that D-3-aminoisobutyrate-pyruvate aminotransferase is identical with alanine-glyoxylate aminotransferase 2, aminolevulinate aminotransferase, 2-aminobutyrate aminotransferase and dimetylarginine-pyruvate aminotransferase.

Alanine↗
PubMed1997

Structure of an alpha-Keto beta-Amido Acid, 3-(Phenylacetamido)pyruvic Acid, and Its Methyl Ester in the Solid State and in Organic and Aqueous Solvents.

3-(Phenylacetamido)pyruvic acid and its methyl ester both exist in the enol form in the solid state and when dissolved in organic solvents. In aqueous solution, the pK(a)'s of the enol acid are 3.28 (CO(2)H) and 10.14 (enolic OH) and that of the ester is 8.14 (enolic OH). The thermodynamically stable form of both acid and ester in aqueous solution, however, is the keto species. Ketonization rates of 3-(phenylacetamido)pyruvic acid were determined spectrophotometrically in acid and in buffered solution at neutral pH. The dominant reaction at low pH is the pH-independent protonation of the enol carboxylate monoanion with a rate constant of 0.062 s(-)(1) M(-)(1). At neutral pH, the ketonization in water alone is very slow but is strongly catalyzed by buffer acids. Rapid, partial (ca. 30%) hydration of the keto form also occurs in aqueous solution. The pK(a) of the pyruvate as a carbon acid is around 12.5. These results are compared with literature data for pyruvic acid itself. Application of peptidyl pyruvates and their derivatives as protease inhibitors requires careful assessment of the complications illustrated by the behavior of 3-(phenylacetamido)pyruvic acid and its methyl ester in aqueous solution.

Journal Article↗
PubMed1976

Purification, characterization and identification of rat liver histidine-pyruvate aminotransferase isoenzymes.

1. Histidine-pyruvate aminotransferase (isoenzyme 1) was purified to homogeneity from the mitochondrial and supernatant fractions of rat liver, as judged by polyacrylamide-gel electrophoresis and isolectric focusing. Both enzyme preparations were remarkably similar in physical and enzymic properties. Isoenzyme 1 had pI8.0 and a pH optimum of 9.0. The enzyme was active with pyruvate as amino acceptor but not with 2-oxoglutarate, and utilized various aromatic amino acids as amino donors in the following order of activity: phenylalanine greater than tyrosine greater than histidine. Very little activity was found with tryptophan and 5-hydroxytryptophan. The apparent Km values were about 2.6mM for histidine and 2.7 mM for phenylalanine. Km values for pyruvate were about 5.2mM with phenylalanine as amino donor and 1.1mM with histidine. The aminotransferase activity of the enzyme towards phenylalanine was inhibited by the addition of histidine. The mol.wt. determined by gel filtration and sucrose-density-gradient centrifugation was approx. 70000. The mitochondrial and supernatant isoenzyme 1 activities increased approximately 25-fold and 3.2-fold respectively in rats repeatedly injected with glucagon for 2 days. 2. An additional histidine-pyruvate aminotransferase (isoenzyme 2) was partially purified from both the mitochondrial and supernatant fractions of rat liver. Nearly identical properties were observed with both preparations. Isoenzyme 2 had pI5.2 and a pH optimum of 9.3. The enzyme was specific for pyruvate and did not function with 2-oxoglutarate. The order of effectiveness of amino donors was tyrosine = phenylalanine greater than histidine greater than tryptophan greater than 5-hydroxytryptophan. The apparent Km values for histidine and phenylalanine were about 0.51 and 1.8 mM respectively. Km values for pyruvate were about 3.5mM with phenylalanine and 4.7mM with histidine as amino donors. Histidine inhibited phenylalanine aminotransferase activity of the enzyme. Gel filtration and sucrose-density-gradient centrifugation yielded a mol.wt. of approx. 90000. Neither the mitochondrial nor the supernatant isoenzyme 2 activity was elevated by glucagon injection.

Animals↗
PubMed2004

Ethyl pyruvate reduces liver injury in a murine model of extrahepatic cholestasis.

Ethyl pyruvate has been shown to ameliorate liver injury and decrease expression of several proinflammatory cytokines when used to treat mice with hemorrhagic shock or alcoholic hepatitis. Herein we sought to determine whether delayed treatment with ethyl pyruvate dissolved in a Ringer's-type balanced salt solution--Ringer's ethyl pyruvate solution (REPS)--would be beneficial in a murine model of common bile duct ligation (CBDL)-induced liver injury. Male C57BL/6 mice were subjected to a sham (n = 6) procedure or CBDL (n = 27). Twenty-four hours after operation, mice subjected to CBDL were randomized to receive treatment with either REPS (40 mg/kg of ethyl pyruvate per dose) or Ringer's lactate solution (RLS) every 8 h over a 72 h period. Compared with sham-treated controls, CBDL in RLS-treated mice was associated with histological evidence of hepatocellular necrosis as well as significant increases in the plasma concentrations of alanine aminotransferase and total bilirubin. Relative to sham-treated controls, CBDL in RLS-treated mice also was associated with increased hepatic lipid peroxidation and increased hepatic expression of transcripts for TNF, IL-6, and iNOS. All of these changes were significantly attenuated by delayed treatment with REPS after CBDL. In the RLS-treated group, CBDL was associated with increased NF-kappaB DNA binding in nuclear extracts prepared from liver tissue. Treatment with REPS increased NF-kappaB DNA binding still further. CBDL was associated with increased hepatocellular apoptosis in both the RLS- and REPS-treated groups. These data support the view that ethyl pyruvate ameliorates hepatic inflammation, lipid peroxidation, and necrosis in mice subjected to CBDL. Ethyl pyruvate warrants further evaluation as an adjunctive treatment to ameliorate liver injury from extrahepatic biliary obstruction.

Alanine Transaminase↗
PubMed1977

Pyruvate dehydrogenase complex from higher plant mitochondria and proplastids.

The pyruvate dehydrogenase complex from pea (Pisum sativum L.) mitochondria was purified 23-fold by high speed centrifugation and glycerol gradient fractionation. The complex had a s(20,w) of 47.5S but this is a minimal value since the complex is unstable. The complex is specific for NAD(+) and pyruvate; NADP(+) and other keto acids give no reaction. Mg(2+), thiamine pyrophosphate, and cysteine are also required for maximal activity. The pH optimum for the complex was between 6.5 and 7.5.Continuous sucrose density gradients were used to separate castor bean (Ricinus communis L.) endosperm proplastids from mitochondria. Pyruvate dehydrogenase complex activity was found to be coincident with the proplastid peak on all of the gradients. Some separation of proplastids and mitochondria could be achieved by differential centrifugation and the ratios of the activities of the pyruvate dehydrogenase complex to succinic dehydrogenase and acetyl-CoA carboxylase to succinic dehydrogenase were consistent with both the pyruvate dehydrogenase complex and acetyl-CoA carboxylase being present in the proplastid. The proplastid fraction has to be treated with a detergent, Triton X-100, before maximal activity of the pyruvate dehydrogenase complex activity is expressed, indicating that it is bound in the organelle. The complex had a sharp pH optimum of 7.5. The complex required added Mg(2+), cysteine, and thiamine pyrophosphate for maximal activity but thiamine pyrophosphate was inhibitory at higher concentrations.

Journal Article↗
PubMed1985

Purification and Characterization of the Pea Chloroplast Pyruvate Dehydrogenase Complex : A Source of Acetyl-CoA and NADH for Fatty Acid Biosynthesis.

The pyruvate dehydrogenase complex has been purified 76-fold, to a specific activity of 0.6 mumoles per minute per milligram protein, beginning with isolated pea (Pisum sativum L. var Little Marvel) chloroplasts. Purification was accomplished by rate zonal sedimentation, polyethyleneglycol precipitation, and ethyl-agarose affinity chromatography. Characterization of the substrates as pyruvate, NAD(+), and coenzyme-A and the products as NADH, CO(2), and acetyl-CoA, in a 1:1:1 stoichiometry unequivocally established that activity was the result of the pyruvate dehydrogenase complex. Immunochemical analysis demonstrated significant differences in structure and organization between the chloroplast pyruvate dehydrogenase complex and the more thoroughly characterized mitochondrial complex. Chloroplast complex has a higher magnesium requirement and a more alkaline pH optimum than mitochondrial complex, and these properties are consistent with light-mediated regulation in vivo. The chloroplast pyruvate dehydrogenase complex is not, however, regulated by ATP-dependent inactivation. The properties and subcellular localization of the chloroplast pyruvate dehydrogenase complex are consistent with its role of providing acetyl-CoA and NADH for fatty acid synthesis.

Journal Article↗
PubMed1988

Synthesis of Glycolate from Pyruvate via Isocitrate Lyase by Tobacco Leaves in Light.

Tobacco (Nicotiana tabacum var Havana Seed) leaf discs were supplied tracer quantities of [2-(14)C]- and [3-(14)C]pyruvate for 60 minutes in steady state photosynthesis with 21% or 1% O(2), and the glycolate oxidase inhibitor alpha-hydroxy-2-pyridinemethanesulfonic acid was then added for 5 or 10 minutes to cause glycolate to accumulate. The [3-(14)C]pyruvate was converted directly to glycolate as shown by a 50% greater than equallabeled (14)C in C-2 of glycolate, and the fraction of (14)C in C-2 increased in 1% O(2) to 80% greater than equal-labeled. This suggests the pathway using pyruvate is less O(2)-dependent than the oxygenase reaction producing glycolate from the Calvin cycle. The formation of glycolate from pyruvate in the leaf discs was time-dependent and with [2-(14)C]- and [3-(14)C]pyruvate supplied leaf discs the C-2 of glyoxylate derived from C-2 of isocitrate was labeled asymmetrically in a manner similar to the asymmetrical labeling of C-2 of glycolate under a number of conditions. Thus glycolate was probably formed by the reduction of glyoxylate. Isocitric lyase activity of tobacco leaves was associated with leaf mitochondria, though most of the activity was in the supernatant fraction after differential centrifugation of leaf homogenates. The total enzyme activity was at least 35 micromoles per gram fresh weight per hour. The relative contribution of the pathway to the glycolate pool is unknown, but the results support the existence of a sequence of reactions leading to glycolate synthesis during photosynthesis with pyruvate, isocitrate, and glyoxylate as intermediates.

Journal Article↗
PubMed1989

Role of Metabolites in the Reversible Light Activation of Pyruvate, Orthophosphate Dikinase in Zea mays Mesophyll Cells in Vivo.

Whole leaf and mesophyll cell concentrations of pyruvate, phosphoenolpyruvate (PEP), ATP, and ADP were determined in Zea mays during the reversible light activation of pyruvate, orthophosphate dikinase in vivo. Mesophyll cell levels of the four metabolites were estimated by extrapolation from values in freeze-quenched leaf samples that were fractionated by differential filtration through nylon mesh nets (adapted from M Stitt, HW Heldt [1985] Planta 164: 179-188). During the 3 minutes required for complete light activation of dikinase, pyruvate levels in the mesophyll cell decreased (from 166 +/- 15 to 64 +/- 10 nanomoles per milligram of chlorophyll [nmol/mg Chl]) while PEP levels increased (from 31 +/- 4 to 68 +/- 4 nmol/mg Chl, with a transient burst of 133 +/- 16 nmol/mg Chl at 1 minute). Mesophyll cell levels of ATP increased (from 22 +/- 4 to 48 +/- 3 nmol/mg Chl) and ADP levels decreased (from 16 +/- 4 to 7 +/- 6 nmol/mg Chl) during the first minute of illumination. Upon darkening of the leaf and inactivation of dikinase, pyruvate levels initially increased in the mesophyll (from 160 +/- 30 to a maximum of 625 +/- 40 nmol/mg Chl), and then slowly decreased to about the initial value in the light over an hour. PEP levels dropped (from 176 +/- 5 to 47 +/- 3 nmol/mg Chl) in the first 3 minutes and remained low for the remainder of the dark period. Mesophyll levels of ATP and ADP rapidly decreased and increased, respectively, about twofold upon darkening. The trends observed for these metabolite levels in the mesophyll cell during the light/dark regulation of pyruvate, orthophosphate dikinase activity suggest that pyruvate and PEP do not play a major role in vivo in regulating the extent of light activation (dephosphorylation) or dark inactivation (ADP-dependent threonyl phosphorylation) of dikinase by its bifunctional regulatory protein. While the changes in ADP levels appear qualitatively consistent with a regulatory role for this metabolite in the light activation and dark inactivation of dikinase, they are not of a sufficient magnitude to account completely for the tenfold change in enzyme activity observed in vivo.

Journal Article↗
PubMed1985

Cloning and expression in Escherichia coli of cDNA for serine: pyruvate aminotransferase of rat liver.

Cloned cDNAs for rat liver serine: pyruvate aminotransferase were obtained by screening of a cDNA expression bank of rat liver with an antibody against the enzyme. Nineteen clones were isolated from 33 000 transformants and most of them had common fragments of cDNA on analysis by digestion with some restriction enzymes. These clones were identified as those containing cDNA for serine:pyruvate aminotransferase by the following criteria. (a) At the nucleic acid level, a 500-base-pair fragment of cDNA prepared by digestion of cDNAs with EcoRI and PstI hybridized with the mRNA coding for serine:pyruvate aminotransferase as judged by hybrid-selected and hybrid-arrested translations. (b) Specific proteins were detected in nine bacterial clones, a 40-kDa protein in one clone and a 39-kDa protein in eight clones. Among them only the 40-kDa protein was found to be solubilized from the cell by sonication, and this protein was immunoprecipitated with an antibody against serine:pyruvate aminotransferase of rat liver. (c) High activity of serine:pyruvate aminotransferase was expressed both in whole cell suspension and sonicated extract prepared from the transformant producing the 40-kDa protein, and 99% of the activity was immunoreactive with the antibody. Two types of mRNA for serine:pyruvate aminotransferase were detected on the RNA blot analysis by using cloned cDNA fragment as a probe. The larger mRNA (approximately 1600 nucleotides) was glucagon-inducible while the smaller one (approximately 1500 nucleotides) was not affected by the hormone.

Animals↗
PubMed1987

Inhibition of lactate production in rat brain extracts and synaptosomes by 3-[4-(reduced 3-pyridine aldehyde-adenine dinucleotide)]-pyruvate.

In basic solutions, pyruvate enolizes and reacts (through its 3-carbon) with the 4-carbon of the nicotinamide ring of NAD+, yielding an NAD-pyruvate adduct in which the nicotinamide ring is in the reduced form. This adduct is a strong inhibitor of lactate dehydrogenase, presumably because it binds simultaneously to the NADH and pyruvate sites. The potency of the inhibition, however, is muted by the adduct's tendency to cyclize to a lactam. We prepared solutions of the pyruvate adduct of NAD+ and of NAD+ analogues in which the -C(O)NH2 of NAD+ was replaced with -C(S)NH2, -C(O)CH3, and -C(O)H. Of the four, only the last analogue, 3-[4-(reduced 3-pyridine aldehyde-adenine dinucleotide)]-pyruvate (RAP) cannot cyclize and it was found to be the most potent inhibitor of beef heart and rat brain lactate dehydrogenases. The inhibitor binds very tightly to the NADH site (Ki approximately 1 nM for the A form). Even at high concentrations (20 microM), RAP had little or no effect on rat brain glyceraldehyde-3-phosphate, pyruvate, alpha-ketoglutarate, isocitrate, soluble and mitochondrial malate, and glutamate dehydrogenases. The glycolytic enzymes, hexokinase and phosphofructokinase, were similarly unaffected. RAP strongly inhibited lactate production from glucose in rat brain extracts but was less effective in inhibiting lactate production from glucose in synaptosomes.

Animals↗
PubMed1990

Effects of indole-pyruvic acid on sleep and food intake in the rat.

Indole-pyruvic acid was studied for its short- and long-term effects on electroencephalographic sleep and on food intake in rats implanted with cortical and muscular electrodes. Following a single injection, indole-pyruvic acid (10-50 mg kg-1 i.p.) reduced by 16-23 min (range) the latency of the first slow-wave episode in a dose-related fashion and produced a significant increase in slow-wave sleep time (12-40%) in doses of 10-30 mg kg-1. Rapid eye movement sleep latency and rapid eye movement sleep time were increased (by 23-37 min) and reduced (57-71%) respectively. The effects of indole-pyruvic acid on slow-wave sleep time were still present after 3, 7 and 14 days of chronic administration (10 mg kg-1 day-1), whereas tolerance to the effect of indole-pyruvic acid on rapid eye movement sleep was observed. Daily food consumption was reduced (20-28%) by acute administration of indole-pyruvic acid (15-30 mg kg-1 i.p.), but tolerance developed after 5 days of repeated injections. These findings are in accordance with previous evidence suggesting that indole-pyruvic acid effects may be related to the activation of central serotonin neurons, which are involved in the inhibitory control of sleep and food intake.

Animals↗
PubMed1992

Conversion of Pyruvate to Acetoin Helps To Maintain pH Homeostasis in Lactobacillus plantarum.

Pyruvate is the substrate for diacetyl and acetoin synthesis by lactobacilli. Exogenous pyruvate stimulates acetoin production when glucose is present as an energy source. In Lactobacillus plantarum ATCC 8014, the energy derived from glucose via glycolysis generated a constant proton motive force of about -120 mV. At a low external pH, energized cells rapidly transported and accumulated pyruvate but did not do so when they were deenergized by nigericin. When large amounts of pyruvate were transported and subsequently accumulated internally, the cotransported protons rapidly lowered the internal pH. The conversion of pyruvate to acetoin instead of acidic end products contributed to the maintenance of pH homeostasis. This is the first report showing that the conversion of pyruvate to acetoin serves as a mechanism of pH homeostasis.

Journal Article↗
PubMed1985

Effects of oxygen on pyruvate formate-lyase in situ and sugar metabolism of Streptococcus mutans and Streptococcus sanguis.

The strictly anaerobic metabolism of sugar in strains of Streptococcus mutans and Streptococcus sanguis was studied because deep layers of dental plaque are strictly anaerobic. Galactose-grown cells of these streptococcal strains had higher pyruvate formate-lyase activity than did glucose-grown cells. Among these strains, two strains of S. mutans had a significantly higher pyruvate formate-lyase activity than did the others. This enzyme is extremely sensitive to oxygen, and even in situ the enzyme was inactivated by exposure of the cells to air. Lactate was less than 50% of the total end product of the strictly anaerobic incubation of the galactose-grown cells of S. mutans with excess glucose, and a significant amount of formate, acetate, and ethanol was produced through the catalysis of pyruvate formate-lyase. But the cells exclusively produced lactate when exposed to air for 2 min before the anaerobic incubation. The metabolism of sorbitol by S. mutans was seriously impaired by the exposure of the cells to oxygen, and the metabolic rate was reduced to less than 1/20 of that found under strictly anaerobic conditions because of the inactivation of pyruvate formate-lyase. S. sanguis produced a smaller amount of the volatile products from glucose than did S. mutans because of the low level of pyruvate formate-lyase. However, the pyruvate formate-lyase in situ in S. sanguis was less sensitive to oxygen than was that in S. mutans. Because of this low sensitivity, S. sanguis metabolized glucose more rapidly under aerobic conditions, whereas the rates of the aerobic and anaerobic metabolism of glucose by S. mutans were similar, which suggests that S. mutans rather than S. sanguis can sustain the rapid sugar metabolism in the deep layers of dental plaque.

Acetyltransferases↗