Acetoin
Acetoin Dehydrogenase
Butanones
Butylene Glycols
Leuconostoc
Fermentation
Acetaldehyde
Alcohol Oxidoreductases
Biochemical and molecular characterization of the Bacillus subtilis acetoin catabolic pathway. (1/91)
A recent study indicated that Bacillus subtilis catabolizes acetoin by enzymes encoded by the acu gene cluster (F. J. Grundy, D. A. Waters, T. Y. Takova, and T. M. Henkin, Mol. Microbiol. 10:259-271, 1993) that are completely different from those in the multicomponent acetoin dehydrogenase enzyme system (AoDH ES) encoded by aco gene clusters found before in all other bacteria capable of utilizing acetoin as the sole carbon source for growth. By hybridization with a DNA probe covering acoA and acoB of the AoDH ES from Clostridium magnum, genomic fragments from B. subtilis harboring acoA, acoB, acoC, acoL, and acoR homologous genes were identified, and some of them were functionally expressed in E. coli. Furthermore, acoA was inactivated in B. subtilis by disruptive mutagenesis; these mutants were impaired to express PPi-dependent AoDH E1 activity to remove acetoin from the medium and to grow with acetoin as the carbon source. Therefore, acetoin is catabolized in B. subtilis by the same mechanism as all other bacteria investigated so far, leaving the function of the previously described acu genes obscure. (+info)Three distinct phases of isoprene formation during growth and sporulation of Bacillus subtilis. (2/91)
During growth on a glucose-tryptone medium, Bacillus subtilis 6051 (Marburg strain) exhibited three phases of isoprene (2-methyl-1, 3-butadiene) formation, corresponding to (i) glucose catabolism and secretion of acetoin, (ii) catabolism of acetoin, and (iii) the early stages of sporulation. These results establish an experimental system for studying the biological role of isoprene formation. (+info)Characterization of a (2R,3R)-2,3-butanediol dehydrogenase as the Saccharomyces cerevisiae YAL060W gene product. Disruption and induction of the gene. (3/91)
The completion of the Saccharomyces cerevisiae genome project in 1996 showed that almost 60% of the potential open reading frames of the genome had no experimentally determined function. Using a conserved sequence motif present in the zinc-containing medium-chain alcohol dehydrogenases, we found several potential alcohol dehydrogenase genes with no defined function. One of these, YAL060W, was overexpressed using a multicopy inducible vector, and its protein product was purified to homogeneity. The enzyme was found to be a homodimer that, in the presence of NAD(+), but not of NADP, could catalyze the stereospecific oxidation of (2R,3R)-2, 3-butanediol (K(m) = 14 mm, k(cat) = 78,000 min(-)(1)) and meso-butanediol (K(m) = 65 mm, k(cat) = 46,000 min(-)(1)) to (3R)-acetoin and (3S)-acetoin, respectively. It was unable, however, to further oxidize these acetoins to diacetyl. In the presence of NADH, it could catalyze the stereospecific reduction of racemic acetoin ((3R/3S)- acetoin; K(m) = 4.5 mm, k(cat) = 98,000 min(-)(1)) to (2R,3R)-2,3-butanediol and meso-butanediol, respectively. The substrate stereospecificity was determined by analysis of products by gas-liquid chromatography. The YAL060W gene product can therefore be classified as an NAD-dependent (2R,3R)-2,3-butanediol dehydrogenase (BDH). S. cerevisiae could grow on 2,3-butanediol as the sole carbon and energy source. Under these conditions, a 3. 5-fold increase in (2R,3R)-2,3-butanediol dehydrogenase activity was observed in the total cell extracts. The isoelectric focusing pattern of the induced enzyme coincided with that of the pure BDH (pI 6.9). The disruption of the YAL060W gene was not lethal for the yeast under laboratory conditions. The disrupted strain could also grow on 2,3-butanediol, although attaining a lesser cell density than the wild-type strain. Taking into consideration the substrate specificity of the YAL060W gene product, we propose the name of BDH for this gene. The corresponding enzyme is the first eukaryotic (2R, 3R)-2,3-butanediol dehydrogenase characterized of the medium-chain dehydrogenase/reductase family. (+info)An operon for a putative ATP-binding cassette transport system involved in acetoin utilization of Bacillus subtilis. (4/91)
The ytrABCDEF operon of Bacillus subtilis was deduced to encode a putative ATP-binding cassette (ABC) transport system. YtrB and YtrE could be the ABC subunits, and YtrC and YtrD are highly hydrophobic and could form a channel through the cell membrane, while YtrF could be a periplasmic lipoprotein for substrate binding. Expression of the operon was examined in cells grown in a minimal medium. The results indicate that the expression was induced only early in the stationary phase. The six ytr genes form a single operon, transcribed from a putative sigma(A)-dependent promoter present upstream of ytrA. YtrA, which possesses a helix-turn-helix motif of the GntR family, acts probably as a repressor and regulates its own transcription. Inactivation of the operon led to a decrease in maximum cell yield and less-efficient sporulation, suggesting its involvement in the growth in stationary phase and sporulation. It is known that B. subtilis produces acetoin as an external carbon storage compound and then reuses it later during stationary phase and sporulation. When either the entire ytr operon or its last gene, ytrF, was inactivated, the production of acetoin was not affected, but the reuse of acetoin became less efficient. We suggest that the Ytr transport system plays a role in acetoin utilization during stationary phase and sporulation. (+info)Bacillus subtilis ccpA gene mutants specifically defective in activation of acetoin biosynthesis. (5/91)
A large number of carbon source utilization pathways are repressed in Bacillus subtilis by the global regulator CcpA, which also acts as an activator of carbon excretion pathways during growth in media containing glucose. In this study, CcpA mutants defective in transcriptional activation of the alsSD operon, which is involved in acetoin biosynthesis, were identified. These mutants retained normal glucose repression of amyE, encoding alpha-amylase, and acsA, encoding acetyl-coenzyme A synthetase, and normal activation of ackA, which is involved in acetate excretion; in these ccpA mutants the CcpA functions of activation of the acetate and acetoin excretion pathways appear to be separated. (+info)Analysis of acetoin and diacetyl in bacterial culture supernatants by gas-liquid chromatography. (6/91)
The acetoin and diacetyl contents of culture supernatants of Voges-Proskauer-positive "viridans" streptotocci, Klebsiella pneumoniae and Staphylococcus aureus, were determined by a gas liquid chromatographic procedure, in which supernatants were extracted with diethyl ether and diacetyl was measured on columns of 10% (wt/wt) polyethylene glycol 400 (PEG 400) at 73 C. Acetoin was converted to diacetyl, before analysis, by a simple oxidation procedure with ferric chloride and without a distillation step. Streptococcal culture supernatants were shown by this method to contain only acetoin; supernatants of K. pneumoniae and S. aureus contained both acetoin and diacetyl. (+info)Mutagenesis at asp27 of pyruvate decarboxylase from Zymomonas mobilis. Effect on its ability to form acetoin and acetolactate. (7/91)
Pyruvate decarboxylase (PDC) is one of several enzymes that require thiamin diphosphate (ThDP) and a bivalent cation as essential cofactors. The three-dimensional structure of PDC from Zymomonas mobilis (ZMPDC) shows that Asp27 (D27) is close to ThDP in the active site, and mutagenesis of this residue has suggested that it participates in catalysis. The normal product of the PDC reaction is acetaldehyde but it is known that the enzyme can also form acetoin as a by-product from the hydroxyethyl-ThDP reaction intermediate. This study focuses on the role of D27 in the production of acetoin and a second by-product, acetolactate. D27 in ZMPDC was altered to alanine (D27A) and this mutated protein, the wild-type, and two other previously constructed PDC mutants (D27E and D27N) were expressed and purified. Determination of the kinetic properties of D27A showed that the affinity of D27A for ThDP is decreased 30-fold, while the affinity for Mg2+ and the Michaelis constant for pyruvate were similar to those of the wild-type. The time-courses of their reactions were investigated. Each mutant has greatly reduced ability to produce acetaldehyde and acetoin compared with the wild-type PDC. However, the effect of these mutations on acetaldehyde production is greater than that on acetoin formation. The D27A mutant can also form acetolactate, whereas neither of the other mutants, nor the wild-type PDC, can do so. In addition, acetaldehyde formation and/or release are reversible in wild-type ZMPDC but irreversible for the mutants. The results are explained by a mechanism involving thermodynamic and geometric characteristics of the intermediates in the reaction. (+info)Regulation of the acetoin catabolic pathway is controlled by sigma L in Bacillus subtilis. (8/91)
Bacillus subtilis grown in media containing amino acids or glucose secretes acetate, pyruvate, and large quantities of acetoin into the growth medium. Acetoin can be reused by the bacteria during stationary phase when other carbon sources have been depleted. The acoABCL operon encodes the E1alpha, E1beta, E2, and E3 subunits of the acetoin dehydrogenase complex in B. subtilis. Expression of this operon is induced by acetoin and repressed by glucose in the growth medium. The acoR gene is located downstream from the acoABCL operon and encodes a positive regulator which stimulates the transcription of the operon. The product of acoR has similarities to transcriptional activators of sigma 54-dependent promoters. The four genes of the operon are transcribed from a -12, -24 promoter, and transcription is abolished in acoR and sigL mutants. Deletion analysis showed that DNA sequences more than 85 bp upstream from the transcriptional start site are necessary for full induction of the operon. These upstream activating sequences are probably the targets of AcoR. Analysis of an acoR'-'lacZ strain of B. subtilis showed that the expression of acoR is not induced by acetoin and is repressed by the presence of glucose in the growth medium. Transcription of acoR is also negatively controlled by CcpA, a global regulator of carbon catabolite repression. A specific interaction of CcpA in the upstream region of acoR was demonstrated by DNase I footprinting experiments, suggesting that repression of transcription of acoR is mediated by the binding of CcpA to the promoter region of acoR. (+info)Acetoin is a chemical compound that is produced as a metabolic byproduct in certain types of bacteria, including some species of streptococcus and lactobacillus. It is a colorless liquid with a sweet, buttery odor and is used as a flavoring agent in the food industry. In addition to its use as a flavoring, acetoin has been studied for its potential antibacterial properties and its possible role in the development of biofilms. However, more research is needed to fully understand the potential uses and implications of this compound.
Acetoin dehydrogenase is an enzyme complex that plays a role in the metabolism of certain organic compounds. It is responsible for catalyzing the oxidation of acetoin to diacetyl, which is then further oxidized to acetate. This enzyme complex is found in many different types of bacteria and is involved in their energy metabolism. Acetoin dehydrogenase is a multi-enzyme complex that consists of several different subunits, including an acetoin reductase, a diacetyl reductase, and a dihydrolipoyl dehydrogenase. These subunits work together to catalyze the oxidation of acetoin in a series of steps. The overall reaction is:
Acetoin + NAD+ -> Diacetyl + NADH + H+
Diacetyl + 2NADH + 2H+ -> 2Acetate + 2NAD+
The overall equation for the conversion of acetoin to acetate by acetoin dehydrogenase is:
Acetoin + NAD+ -> 2Acetate + NADH + H+
This reaction is important in the metabolism of certain types of bacteria, as it allows them to generate energy and reduce power for their growth and survival.
Butanones are a group of chemical compounds that contain a ketone functional group and have the molecular formula C4H8O. They are also known as methyl ethyl ketones or MEKs. The simplest butanone is called methyl ethyl ketone (MEK) or 2-butanone, which has a chain of four carbon atoms with a ketone group in the second position. Other butanones include diethyl ketone (3-pentanone), which has a ketone group in the third position, and methyl isobutyl ketone (MIBK) or 4-methyl-2-pentanone, which has a branched chain with a ketone group in the second position.
Butanones are commonly used as solvents in various industrial applications, such as paint thinners, adhesives, and cleaning agents. They have a characteristic odor and can be harmful if ingested or inhaled in large quantities. Exposure to butanones can cause irritation of the eyes, skin, and respiratory tract, and prolonged exposure may lead to neurological symptoms such as dizziness, headache, and nausea.
Butylene glycols are a type of organic compounds that belong to the class of diols, which are chemical compounds containing two hydroxyl groups. Specifically, butylene glycols are composed of a four-carbon chain with two hydroxyl groups located on adjacent carbon atoms.
There are two isomeric forms of butylene glycol: 1,2-butanediol and 1,3-butanediol.
* 1,2-Butanediol (also known as 1,2-butylene glycol) has the hydroxyl groups on the first and second carbon atoms of the chain. It is a colorless, viscous liquid that is used as a solvent, humectant, and antifreeze in various industrial and cosmetic applications.
* 1,3-Butanediol (also known as 1,3-butylene glycol) has the hydroxyl groups on the first and third carbon atoms of the chain. It is also a colorless, viscous liquid that is used as a solvent, humectant, and antifreeze in various industrial and cosmetic applications.
Butylene glycols are generally considered to be safe for use in cosmetics and other consumer products, although they may cause skin irritation or allergic reactions in some individuals. They are also used as intermediates in the synthesis of other chemicals, such as polyesters and polyurethanes.
Diacetyl is a volatile, yellow-green liquid that is a byproduct of fermentation and is used as a butter flavoring in foods. The chemical formula for diacetyl is CH3COCH3. It has a buttery or creamy taste and is often added to microwave popcorn, margarine, and other processed foods to give them a buttery flavor.
Diacetyl can also be found in some alcoholic beverages, such as beer and wine, where it is produced naturally during fermentation. In high concentrations, diacetyl can have a strong, unpleasant odor and taste.
There has been concern about the potential health effects of diacetyl, particularly for workers in factories that manufacture artificial butter flavorings. Some studies have suggested that exposure to diacetyl may increase the risk of developing lung disease, including bronchiolitis obliterans, a serious and sometimes fatal condition characterized by scarring and narrowing of the airways in the lungs. However, more research is needed to fully understand the health effects of diacetyl and to determine safe levels of exposure.
Leuconostoc is a genus of gram-positive, facultatively anaerobic bacteria that belong to the family Leuconostocaceae. These bacteria are non-motile, non-spore forming, and occur as pairs or chains. They are catalase-negative and reduce nitrate to nitrite.
Leuconostoc species are commonly found in nature, particularly in plants, dairy products, and fermented foods. They play a significant role in the food industry, where they are used in the production of various fermented foods such as sauerkraut, pickles, and certain cheeses.
In clinical settings, Leuconostoc species can sometimes be associated with healthcare-associated infections, particularly in patients who have underlying medical conditions or who are immunocompromised. They can cause bacteremia, endocarditis, and device-related infections. However, these infections are relatively rare, and the majority of Leuconostoc species are considered to be non-pathogenic.
Fermentation is a metabolic process in which an organism converts carbohydrates into alcohol or organic acids using enzymes. In the absence of oxygen, certain bacteria, yeasts, and fungi convert sugars into carbon dioxide, hydrogen, and various end products, such as alcohol, lactic acid, or acetic acid. This process is commonly used in food production, such as in making bread, wine, and beer, as well as in industrial applications for the production of biofuels and chemicals.
Acetaldehyde is a colorless, volatile, and flammable liquid with a pungent odor. It is the simplest aldehyde, with the formula CH3CHO. Acetaldehyde is an important intermediate in the metabolism of alcohol and is produced by the oxidation of ethanol by alcohol dehydrogenase. It is also a naturally occurring compound that is found in small amounts in various foods and beverages, such as fruits, vegetables, and coffee.
Acetaldehyde is a toxic substance that can cause a range of adverse health effects, including irritation of the eyes, nose, and throat, nausea, vomiting, and headaches. It has been classified as a probable human carcinogen by the International Agency for Research on Cancer (IARC). Long-term exposure to acetaldehyde has been linked to an increased risk of certain types of cancer, including cancers of the oral cavity, esophagus, and liver.
Alcohol oxidoreductases are a class of enzymes that catalyze the oxidation of alcohols to aldehydes or ketones, while reducing nicotinamide adenine dinucleotide (NAD+) to NADH. These enzymes play an important role in the metabolism of alcohols and other organic compounds in living organisms.
The most well-known example of an alcohol oxidoreductase is alcohol dehydrogenase (ADH), which is responsible for the oxidation of ethanol to acetaldehyde in the liver during the metabolism of alcoholic beverages. Other examples include aldehyde dehydrogenases (ALDH) and sorbitol dehydrogenase (SDH).
These enzymes are important targets for the development of drugs used to treat alcohol use disorder, as inhibiting their activity can help to reduce the rate of ethanol metabolism and the severity of its effects on the body.
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