SEARCH · PubMed Health

Results for “Laurates”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 recordsLinked to original sources

PubMed1999

Lysophosphatidic acid acyltransferase from coconut endosperm mediates the insertion of laurate at the sn-2 position of triacylglycerols in lauric rapeseed oil and can increase total laurate levels

Expression of a California bay laurel (Umbellularia californica) 12:0-acyl-carrier protein thioesterase, bay thioesterase (BTE), in developing seeds of oilseed rape (Brassica napus) led to the production of oils containing up to 50% laurate. In these BTE oils, laurate is found almost exclusively at the sn-1 and sn-3 positions of the triacylglycerols (T.A. Voelker, T.R. Hayes, A.C. Cranmer, H.M. Davies [1996] Plant J 9: 229-241). Coexpression of a coconut (Cocos nucifera) 12:0-coenzyme A-preferring lysophosphatitic acid acyltransferase (D.S. Knutzon, K.D. Lardizabal, J.S. Nelsen, J.L. Bleibaum, H.M. Davies, J.G. Metz [1995] Plant Physiol 109: 999-1006) in BTE oilseed rape seeds facilitates efficient laurate deposition at the sn-2 position, resulting in the acccumulation of trilaurin. The introduction of the coconut protein into BTE oilseed rape lines with laurate above 50 mol % further increases total laurate levels.

Journal Article↗

PubMed1997

Fatty acid distribution and lipid metabolism in developing seeds of laurate-producing rape (Brassica napus L.).

The fatty acid composition and content of membrane and storage lipids of two transgenic laurate-producing rape (Brassica napus L.) lines were monitored during seed development. The two lines, the medium-laurate (ML) line and the high-laurate (HL) line, accumulated 34 mol% and 55 mol% of laurate in their seed triacylglycerols, respectively. The diacylglycerols contained about 17 and 33 mol% of laurate in the ML- and HL-lines, respectively, from the mid-stage of seed development up to seed maturity. The ML-line showed a maximal relative laurate content in phosphatidylcholine (17 mol%) at the mid-stage of seed development whereafter the content decreased to 2.7 mol% with seed maturity. The laurate content in phosphatidylcholine was observed to remain high (26 mol%) in the HL-line from the mid-stage to the end of triacylglycerol deposition. Thereafter, the relative content decreased and reached 6.6 mol% in the mature seeds. There was an enhanced activity of lauroyl-phosphatidylcholine-metabolizing enzymes in the seed membranes from laurate-producing lines compared with control lines, which might explain the decrease seen in laurate content in phosphatidylcholine during seed maturation. A comparison of the laurate distribution in the lipids from developing laurate-producing rape seeds and developing seeds from three species naturally accumulating laurate at similar levels revealed differences in laurate metabolism compared with these species. The results suggest that phospholipids and triacylglycerols are synthesized from the same diacylglycerol pool in rape seeds and that rape lysophosphatidic acid acyltransferase and diacylglycerol acyltransferase do not have the same preference for laurate substrates as the corresponding enzymes in seed tissues naturally accumulating this acyl group. In addition, the mechanisms that specifically remove or exclude laurate from membrane lipids appear less effective in rape seed than in tissues naturally evolved to synthesize laurate-rich oils.

Brassica↗

PubMed2000

Comparative study on uncoupling effects of laurate and lauryl sulfate on rat liver and skeletal muscle mitochondria.

Uncoupling effects of laurate and lauryl sulfate have been studied in the isolated rat liver and skeletal muscle mitochondria. In the oligomycin-treated liver mitochondria, 0.02 mM laurate or 0.16 mM lauryl sulfate caused a two-fold stimulation of respiration, accompanied by a membrane potential decrease. Carboxyatractylate (CAtr) and glutamate (or aspartate) strongly decrease the effect of laurate and lauryl sulfate on respiratory rate and membrane potential (the recoupling effect). With both uncouplers, this effect is maximal for CAtr and glutamate (aspartate) at pH 7.8 and 7.0, respectively. Tetraphenyl phosphonium cations, which decrease negative membrane charges, cause an alkaline shift of these pH dependences. Small amounts of lauryl sulfate, which increase the membrane negative charge, induce the opposite shift when laurate is used as an uncoupler. ADP, but not GDP, partially recouple with both laurate and lauryl sulfate. We conclude that lauryl sulfate-induced uncoupling in rat liver, like the uncoupling induced by laurate, is mediated by the ATP/ ADP and glutamate/aspartate antiporters. In skeletal muscle mitochondria uncoupled by laurate, 200 microM GDP causes partial recoupling which can be enhanced by a subsequent additions of CAtr, glutamate and serum albumin. CAtr added before GDP promotes a larger recoupling than when added after GDP and prevents the subsequent effect of GDP. ADP is effective as recoupler at lower concentrations that GDP, whereas CDP is without influence. Lauryl sulfate uncoupling of skeletal muscle mitochondria is GDP-resistant but is sensitive to ADP, CAtr, glutamate and serum albumin. Our data suggest that in skeletal muscle mitochondria a GDP-sensitive mechanism is involved in uncoupling induced by laurate. This mechanism is absent in liver mitochondria. Possible mechanisms of laurate and lauryl sulfate-induced uncoupling are discussed.

Adenosine Triphosphate↗

PubMed1996

Sucrose laurate gels as a percutaneous delivery system for oestradiol in rabbits.

In this study sucrose laurate was formulated in hydrogels and investigated as a suitable transdermal penetration enhancer for oestradiol. Using rabbits as an animal model, the absolute bioavailability and the skin irritation were evaluated after single and multiple application. Three hydrogels containing 60 mg% oestradiol were evaluated: Oestrogel, and two hypromellose gels containing 5 and 15% sucrose laurate (w/w), respectively. No stability problem of the sucrose laurate was detected during a storage period of four months at 7 +/- 2 degrees C. After single application no significant difference (P < 0.05) was observed between the bioavailability parameters of Oestrogel and the 5% sucrose laurate gel. The values obtained for the 15% sucrose laurate gel were significantly higher than for the other gels. When applied on day 7 after a 6-day treatment, twice daily with the respective placebo gel, no significant difference was seen amongst the three formulations for any of the parameters evaluated. When the results after multiple application were compared with those after single application, a significant increase in oestradiol bioavailability was seen for the gel containing 30% ethanol and a significant decrease in oestradiol bioavailability was seen for the 5 and 15% sucrose laurate gels. Histological evaluation of the untreated and treated skin biopsies, showed a significantly higher incidence of infiltrate for all treated skin biopsies in comparison with the untreated ones. A significant increase in skinfold thickness was seen for the skin biopsies treated with gel containing 15% sucrose laurate. It can be concluded that sucrose laurate shows a potential as an absorption enhancer for percutaneous drug delivery.

Administration, Cutaneous↗

PubMed1989

Pyrenemethyl laurate, a new fluorescent substrate for continuous kinetic determination of lipase activity.

A fluorescent acyl derivative of pyrenemethanol, pyrenemethyl laurate, was synthesized and used for the determination of several lipases by a continuous kinetic assay. The influence of the physical parameters of the substrate (pyrenemethyl laurate) and its hydrolysis product (pyrenemethanol), on the fluorescence emission was studied. The hydrolysis of pyrenemethyl laurate could be monitored directly in a spectrofluorometer because of the very high monomeric emission of pyrenemethanol at about 375 nm, whereas an aqueous dispersion of pyrenemethyl laurate emitted at 475 nm ('excimeric'). Pyrenemethyl laurate was hydrolyzed by gastric lipase, cellular lipases of haemopoietic cells, and the bacterial lipase of Rhizopus arrhizus.

Fluorescent Dyes↗

PubMed1996

High-affinity binding of laurate to naturally occurring mutants of human serum albumin and proalbumin.

Binding of laurate (n-dodecanoate) to genetic variants of albumin or its proprotein and to normal albumin isolated from the same heterozygous carriers was studied by a kinetic dialysis technique at physiological pH. The first stoichiometric association constant for binding to proalbumin Lille (Arg-2-->His) and albumin (Alb) Roma (Glu321-->Lys) was increased to 126% and 136% respectively compared with that for binding to normal albumin, whereas the constant for Alb Maku (Lys541-->Glu) was decreased to 80%. In contrast, normal laurate-binding properties were found for as many as nine other albumin variants with single amino acid substitutions. Because the net charges of all these mutants were different from that of normal albumin, the results suggest that the examples of modified laurate binding are not caused by long-range electrostatic effects. Rather, the three positions mentioned are located close to different binding sites for the fatty acid anion. The most pronounced effect was observed for the glycosylated Alb Casebrook, the binding constant of which was decreased to 20%. Binding to the glycosylated Alb Redhill was also decreased, but to a smaller extent (68%). These decreases in binding are caused by partial or total blocking of the high-affinity site by the oligosaccharides, by the negative charges of the oligosaccharides, and/or by conformational changes induced by these bulky moieties. Laurate binding to two chain-termination mutants (Alb Catania and Alb Venezia) was normal, indicating that the C-terminus of albumin is not important for binding. By using different preparations of normal albumin as controls in the binding experiments, it was also possible to compare the effect of various methods for isolation and defatting on laurate binding.

Amino Acid Sequence↗

PubMed1994

Endotoxin biosynthesis in Pseudomonas aeruginosa: enzymatic incorporation of laurate before 3-deoxy-D-manno-octulosonate.

Unlike Escherichia coli, living cells of Pseudomonas aeruginosa can complete the fatty acylation of lipid A when the biosynthesis of 3-deoxy-D-manno-octulosonate (Kdo) is inhibited (R. C. Goldman, C. C. Doran, S. K. Kadam, and J. O. Capobianco, J. Biol. Chem. 263:5217-5233, 1988). In this study, we demonstrate the presence of a novel enzyme in extracts of P. aeruginosa that can transfer lauroyl-acyl carrier protein (ACP) to a tetraacyl disaccharide-1,4'-bis-phosphate precursor of lipid A (termed lipid IVA) that accumulates in Kdo-deficient mutants of E. coli. Comparable E. coli extracts cannot transfer laurate from lauroyl-ACP to lipid IVA, only to (Kdo)2-lipid IVA (K. A. Brozek, and C. R. H. Raetz, J. Biol. Chem. 265:15410-15417, 1990). P. aeruginosa extracts do not utilize myristoyl- or R-3-hydroxymyristoyl-ACP instead of lauroyl-ACP to acylate lipid IVA. Laurate incorporation in P. aeruginosa extracts is dependent upon time, protein concentration, and the presence of Triton X-100 but is inhibited by lauroyl-coenzyme A. P. aeruginosa extracts transfer only one laurate to lipid IVA, whereas E. coli extracts can transfer two laurates to (Kdo)2-lipid IVA. These results demonstrate that incorporation of laurate into lipid A does not require prior attachment of Kdo in all gram-negative bacteria.

ADP Ribose Transferases↗

PubMed1983

Effects of starvation on microsomal cytochrome P-450 and laurate-omega-hydroxylation of rat kidney and liver.

Cytochrome P-450 (P-450) content and laurate-omega-oxidation activity in rat kidney and liver microsomes were investigated following starvation. Multiple forms of P-450 were analyzed by one dimensional separation using peroxidase stained SDS-continuous gradient polyacrylamide gel electrophoresis. Gels of the hepatic microsomes treated with phenobarbital showed three P-450 bands, and the renal microsomes showed one sharp band, which was induced remarkably by starvation and coincided with the middle molecular form of P-450 from the hepatic microsomes. Since laurate-omega-oxidation activity was induced specifically by starvation but not by drug treatment, in both the kidney and the liver microsomes, the middle molecular form of P-450 might catalyze laurate-omega-oxidation. It seemed, therefore, that a special P-450 subunit catalyzing laurate-omega-oxidation has a greater function in the renal rather than hepatic microsomes because the specific laurate-omega-oxidation activity per starvation induced P-450 content was relatively similar in both the kidney and the liver.

Animals↗

PubMed2002

Development of an ethyl laurate-based microemulsion for rapid-onset intranasal delivery of diazepam.

An ethyl laurate-based microemulsion system with Tween 80 as surfactant, propylene glycol and ethanol as cosolvents was developed for intranasal delivery of diazepam. Phase behavior and solubilization capacity of the microemulsion system were characterized and in vivo nasal absorption of diazepam from microemulsion formulations was investigated in rabbits. A single isotropic region, which is considered as a bicontinuous microemulsion, was found in the pseudo-ternary phase diagrams developed at various Tween 80: propylene glycol: ethanol ratios. With the increase of Tween 80 concentration, the microemulsion region area, microemulsion viscosity, and the amount of H(2)O and ethyl laurate solubilized into the microemulsion system increased; however, the increase of ethanol percentage produced opposite effects. Diazepam, a practically water-insoluble drug, displayed a high solubility of 41 mg/ml in a microemulsion consisting of 15% ethyl laurate, 15% H(2)O, and 70% (w/w) surfactant/cosurfactant (Tween 80:propylene glycol:ethanol at 1:1:1 weight ratio). Nasal absorption of diazepam from this microemulsion was found to be fairly rapid. At 2 mg/kg dose, the maximum drug plasma concentration was arrived within 2-3 min, and the bioavailability (0-2 h) after nasal spray compared with intravenous injection was about 50%. These results suggest that this ethyl laurate-based microemulsion may be a useful approach for the rapid-onset delivery of diazepam during the emergency treatment of status epilepticus.

Administration, Intranasal↗

PubMed1986

Laurate binding to human serum albumin. Multiple binding equilibria investigated by a dialysis exchange method.

Multiple binding of laurate (n-dodecanoate) to human serum albumin was studied by a kinetic dialysis method. With this method the concentration of unbound ligand can be determined by measuring the rate of exchange of radioactive label across a dialysis membrane under conditions of equilibrium. Determination of the rate constant of exchange, in the absence of albumin, revealed that laurate does not change its state of aggregation over a concentration range from 0.1 microM to 500 microM, indicating the prevalence of a monomer. Binding of laurate to albumin, at pH 7.5, 37 degrees C, was investigated through 220 determinations of binding equilibria in the range of 0-10 mol laurate/mol albumin, corresponding to a concentration range of unbound laurate from 1 nM to 0.1 mM. Binding data were analyzed in terms of stepwise binding. Considering the stochastic errors of the experimental data, we generated a variety of possible (equal goodness of fit) solutions to the stoichiometric binding equation. This analysis resulted in reasonably well-defined values for the first two step constants, with an indication of negative interaction. The variation of the higher step constants excluded any mechanistic conclusions, although the binding isotherms, defined by these varying sets of binding constants, fitted the experimental data well within a chosen probability limit.

Dialysis↗

PubMed1988

Multiple binding of bilirubin to human serum albumin and cobinding with laurate.

Numerical analysis of multiple binding of two ligands to one carrier has been accomplished, using the principle of several sets of acceptable binding constants, with bilirubin-laurate-albumin as an example. Binding of bilirubin to defatted human serum albumin was investigated by a spectroscopic method, based upon a difference of light absorption spectrum for free and bound bilirubin. The observations were supplemented with previous data from an independent technique, measurement of oxidation rates of free bilirubin with hydrogen peroxide and peroxidase. A continuous isotherm was obtained, showing binding of at least 4 mol bilirubin per mole albumin with the following stoichiometric binding constants, 1.11 X 10(8), 1.7 X 10(7), 8 X 10(5), and 4 X 10(4) M-1 at pH 8.2, ionic strength 0.15 M, 25 degrees C. The binding is anticooperative at all steps. A saturation level was not reached. Cobinding of bilirubin and laurate was studied, with up to 2 mol of each ligand per mole albumin, using the peroxidase method for determination of free equilibrium concentrations of bilirubin, and a dialysis rate technique for free laurate. The findings could be described in terms of a stoichiometric model. Heterotropic cooperativity was present among the first bilirubin and the first and second laurate molecules. More than two molecules of either ligand can be bound at the same time.

Bilirubin↗

PubMed1990

Replacing the carboxy-terminal 28 residues of rabbit liver P-450 (laurate (omega-1)-hydroxylase) with those of P-450 (testosterone 16 alpha-hydroxylase) produces a new stereospecific hydroxylase activity.

cDNA for chimeric P-450 consisting of the amino-terminal 462 residues of P-450 (laurate (omega-1)-hydroxylase) and the remaining 28 residues of P-450 (testosterone 16 alpha-hydroxylase) was constructed and expressed in yeast cells. The resulting chimera could catalyze laurate (omega-1)-hydroxylation and benzphetamine N-demethylation at much higher rates than the parental P-450s, but exhibited the same specificity towards fatty acid substrates as the wild-type laurate hydroxylase. When testosterone was examined as a substrate, the 16 beta-hydroxylated product, which cannot be formed by either of the parental P-450s, was detected, suggesting that the laurate hydroxylase contains a structure that is capable of binding testosterone at a proper orientation so that it can be hydroxylated at the 16 beta position.

Amino Acid Sequence↗

PubMed1996

Function of the htrB high temperature requirement gene of Escherichia coli in the acylation of lipid A: HtrB catalyzed incorporation of laurate.

By assaying lysates of Escherichia coli generated with the hybrid lambda bacteriophages of an ordered library (Kohara, Y., Akiyama, K., and Isono, K. (1987) Cell 50, 495-508), we identified two clones (lambda232 and lambda233) capable of overexpressing the lauroyl transferase that functions after 3-deoxy-D-manno-octulosonic acid (Kdo) addition in lipid A biosynthesis (Brozek, K. A., and Raetz, C. R. H. (1990) J. Biol. Chem. 265, 15410-15417). The E. coli DNA inserts in lambda232 and lambda233 suggested that a known gene (htrB) required for rapid growth above 33 degrees C might encode the lauroyl transferase. Using the intermediate (Kdo)2-lipid IVA as the laurate acceptor, extracts of strains with transposon insertions in htrB were found to contain no lauroyl transferase activity. Cells harboring hybrid htrB+ plasmids overproduced transferase activity 100-200-fold. The overproduced transferase was solubilized with a non-ionic detergent and purified further by DEAE-Sepharose chromatography. With lauroyl acyl carrier protein as the donor, the purified enzyme rapidly incorporated one laurate residue into (Kdo)2-lipid IVA. The rate of laurate incorporation was reduced by several orders of magnitude when either one or both Kdos were absent in the acceptor. With a matched set of acyl-acyl carrier proteins, the enzyme incorporated laurate 3-8 times faster than decanoate or myristate, respectively. Transfer of palmitate, palmitoleate, or R-3-hydroxymyristate was very slow. Taken together with previous studies, our findings indicate that htrB encodes a key, late functioning acyltransferase of lipid A biosynthesis.

Acylation↗

PubMed1998

Utility of isolated hepatocytes and radio-HPLC-MSn for the analysis of the metabolic fate of 19-nortestosterone laurate in cattle.

The metabolic fate of 19-nortestosterone laurate in cattle was investigated to evaluate target analyte(s) appropriate to surveillance for illicit use as a growth promoting agent. Bovine hepatocytes were incubated with either [3H]19-nortestosterone laurate (19-NTL; 4-estren-17 beta-laurate-3-one) or [3H]19-nortestosterone (19-NT; 4-estren-17 beta-ol-3-one; nandrolone). Hepatocyte medium was extracted with solid phase C18 media and analysed by narrow bore radio-HPLC-MSn (LCQ, Finnigan) to evaluate the structure of metabolites of 19-NTL and 19-NT. Radio-HPLC of hepatocyte medium extracts following incubation with [3H]19-NTL confirmed that the first step of biotransformation in liver was hydrolysis of the fatty acid ester to release [3H]19-NT, which, in turn, was converted into a range of metabolites of diverse polarity. Hydrolysis of hepatocyte medium extracts with beta-glucuronidase (Helix pomatia) indicated that some of these metabolites were glucuronide or sulfate conjugates. Structural analysis of unconjugated metabolities by positive-ion atmospheric pressure chemical ionisation MS2 and comparison with available reference preparations indicated biotransformation of 19-NT to 4-estren-17 alpha-ol-3-one, 4-estren-3, 17-dione (major metabolite after 1 h), n-hydroxy-4-estren-3, 17-dione, n-hydroxy-4-estren-17-ol-3-one, 5 beta-estran-3 alpha-ol-17-one (noretiocholanolone) and 5 beta-estran-3 alpha, 17 beta-ol (major metabolite after 4 h). Conjugated metabolites were analysed by electrospray ionization, which revealed the presence of glucuronide conjugates of alpha-(trace) and beta-epimers of 19-NT, n-hydroxy-4-estren-3, 17-dione, n-hydroxy-4-estren-17-ol-3-one and 5 beta-estran-3 alpha, 17 beta-diol. These studies provide a clear indication of the route of hepatic metabolism in the bovine, which may now be readily substantiated by reference to samples, such as urine or bile, derived from animals treated with unlabelled 19-NTL.

Anabolic Agents↗

PubMed1989

Identification of regions functioning in substrate interaction of rabbit liver cytochrome P-450 (laurate (omega-1)-hydroxylase).

The nucleotide sequence of cDNA for rabbit liver cytochrome P-450 (laurate (omega-1) hydroxylase) was replaced with that for rabbit liver cytochrome P-450 (testosterone 16 alpha-hydroxylase) in various regions coding for the amino acid sequence between residues 43 and 261. Six chimeric cDNAs thus constructed were cloned into expression vector pAAH5, and expressed in Saccharomyces cerevisiae AH22 cells under the control of yeast ADH1 promoter. Chimeric P-450s synthesized in the transformed yeast cells were purified partially and their catalytic and spectral properties were examined and compared with those of the chimeric P-450 which is considered to possess the same catalytic properties as the wild-type P-450. In the oxidized state the chimeric P-450s exhibited a low-and high-spin mixed-type absorption spectrum of cytochrome P-450 and the spectrum was converted to a typical high-spin type on addition of laurate or caprate, indicating the binding of the fatty acids to the substrate site of the chimeric P-450s. However the affinities of the fatty acids for the chimeras devoid of the sequence of P-450 (laurate (omega-1)-hydroxylase) in either of the regions spanning residues 90-125 and 210-261 were 10 to 20 times lower than those for the chimeras containing the sequence of the wild-type P-450 in both regions. The latter chimeras have about the same affinities as the chimera which is essentially the wild-type P-450.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1981

Induction and specificity of a (cytochrome P-450)-dependent laurate in-chain-hydroxylase from higher plant microsomes.

The substrate and product specifities of the (cytochrome P-450)-dependent laurate monooxygenase from tuber tissues of Jerusalem artichoke (Helianthus tuberosus L.) were investigated. The plant enzyme appeared strictly specific for the C12 free fatty acid and produced a mixture of C-8, C-9 and C-10 hydroxylated lauric acids, the C-9 derivative being predominant. No C-12 or C-11 hydroxylated laurates were detected. The activity of the enzyme, which was not detectable in the intact tuber, was induced by slicing and aging the tissues on water, and strongly superinduced by the addition of manganese and phenobarbital to the aging medium. Regulation of laurate hydroxylase was clearly independent from that of cinnamic acid 4-hydroxylase, another plant cytochrome P-450 enzyme.

Cytochrome P-450 Enzyme System↗

PubMedDate not supplied

Incorporation of label from acetate and laurate into the mannan of Leishmania donovani via the glyoxylate cycle.

Leishmania donovani promastigotes in late-stationary phase incorporated label from [2-14C]acetate and [1-14C]laurate into the mannose residues of mannan, thus confirming the presence of a functional glyoxylate bypass in these parasitic protozoa. Isolated, washed calls also incorporated label from [2-14C]acetate and [1-14C]laurate into mannan during a 1-hr incubation in buffer. Glucose had no effect on label incorporation into mannan, but glutamate caused over a four-fold increase in incorporation from [2-14C]acetate and a 2.4-fold increase from [1-14C]laurate. Staurosporine, a protein kinase inhibitor that inhibits glutamate and alanine oxidation, did not inhibit label incorporation from [2-14C]acetate into mannan. Hyperosmolality caused about a 33% inhibition of label incorporation into mannan. These results show the glyoxylate cycle and/or the subsequent biosynthetic pathway from fructose-6-phosphate to mannan are subject to regulation.

Acetates↗

PubMed1994

Reduction in acid tolerance of Streptococcus downeii by fluoride and potassium laurate.

Streptococcus downeii MFe28 maintains a transmembrane pH gradient at low extracellular pH values using energy from glucose metabolism. The metabolic activity was measured in saturating glucose solutions using a pH-stat, and results were expressed as rates of titratable acid production at defined pH values. The tolerance to acid shock was studied in terms of the ability of cells to resume acid production at pH 8.0 following short-term exposure to low-pH environments. The results with control cells showed an optimum rate of acid production at pH 8.0. The activity extended to pH 4.5 with a half-maximal rate at pH 5.4. Addition of carbonyl cyanide-m-chlorophenylhydrazone, potassium laurate, or potassium fluoride inhibited acid production at lower but not at higher pH values. Inhibition by carbonyl cyanide-m-chlorophenylhydrazone and fluoride was found to be fully reversible at pH 8.0 when compared to control cells. In contrast, laurate inhibited irreversibly at pH values of 6.0 and below. The acid tolerance of S. downeii was severely compromised by laurate, and this action could be useful in dental caries control.

Acids↗