Alcohol in men vs women; women are….
more affected by alcohol than men
Why are women more affected by alcohol than men
1) they are smaller (less total body mass)
2) have less water to dilute alcohol (bc they are more % fat; lean muscle is 75% water, fat tissue is 15% water) per body weight
3) have less ADH in stomach lining (consumes 10% of ethanol vs 30% for men) making them more sensitive to alcohol
Nutrition of Alcohol
Alcohol damages what organs?
all organs in the body
In US for 18-24 year olds how many deaths/injuries are there?
>1,000 deaths and 500,000 injuries due to alcohol related accidents
What can hide alcoholic content?
4 or more drinks for women and 5 or more drinks for men in 2 hrs
Result of binge drinking
can lead to acute alcohol intoxicaion and death
Absorption of Ethanol
1. Absorbed in stomach and small intestine => blood system
2. Food in stomach slows absorption
3. BAC increases
BAC of 0.08 means
0.08% alcohol in blood or 8×10^-4 g/mL blood
What does BAC depend on?
1. how many drinks you have
2. body size
4. Time since ingestion
What BAC is driving impaired
Legal limit in CA
What do cells phones affect; does handheld or handsfree do this?
increase rate of injury crashes by 4 times; both handsfree and hand held
Pathways for alcohol metabolism
1. ADH pathway
2. MEOS pathway (Microsomal Ethanol Oxidizing System (MEOS) is an alternate pathway of ethanol metabolism that )
Metabolism (ADH Pathway) where does it occur?
1. Occurs in liver (70-90%)
2. Occurs in stomach (10-30%)
3. Occurs in cell cytosol; yields energy
Metabolism (ADH Pathway)
Ethanol => use alcohol dehydrogenase => acetylaldhyde => use aldehyde dehydrogenate => acetic acid => use CoA + Ac-CoA => TCA cycle => ATP => Fat via lipgenesis
What else gives rise to Acetyl-CoA?
1. Glucose => Fructose => acetyl-CoA
3. FA oxidation
4. Ketogenic AA
5. Acetyl-CoA give rise to ketone bodies
2 Isoforms enzymes
cytosol high km (indication of protein activity)
mito low km
=> common mutation in East Asian Population => flushing and hangover
=> Drug target for alcoholics
Km is the amount of substrate that produces the half of the maximum velocity of the enzyme.
MEOS pathway used when
1. When ADH can no longer be used, this is the second pathway for alcohol detoxification
How does MEOS work?
1. bypasses ADH
2. Uses NADPH, oxygen, and MEOS (Microsomal Ethanol Oxidizing System) to produce acetylaldehyde and NADP+ and water
cytochrome P450 mono oxygenase (Cyt P450)
MEOS cytochrome P450 contains
heme group (Fe)
Equation for MEOS
RH + O2 + NADPH => ROH + H2O + NADP+
Why is MEOS important?
remove toxins (xenobiotics) and affect drug metabolism
What is alcohol’s effect on p450?
1. Alcohol competitively inhibits sedative detoxification
2. Acetaminophen => use p450 => liver toxin
Alcohol competitively inhibits sedative detoxification
Take a lot of sedative with alcohol can lead to death
Acetaminophen => use p450 => liver toxin
1. This process is stimulated/enhanced by alcohol
2. Increase cyt P450=> cause problems in body
Effects of alcohol
1. Alcohol interacts with endorphins receptors => increase dopamine
2. Alcohol depress CNS => decrease in respiration and heart rate
3. Alcohol can be addictive (esp. in US)
4. Alcohol intake can lead to tolerance => can increase consumption => can lead to dependence and addition
Genetic evidence from comparisons of multiple organisms showed that a glutathione-dependent formaldehyde dehydrogenase, identical to a class III alcohol dehydrogenase (ADH-3/ADH5), is presumed to be the ancestral enzyme for the entire ADH family. Early on in evolution, an effective method for eliminating both endogenous and exogenous formaldehyde was important and this capacity has conserved the ancestral ADH-3 through time. Gene duplication of ADH-3, followed by series of mutations, the other ADHs evolved.
The ability to produce ethanol from sugar (which is the basis of how alcoholic beverages are made) is believed to have initially evolved in yeast. Though this feature is not adaptive from an energy point of view, by making alcohol in such high concentrations so that they would be toxic to other organisms, yeast cells could effectively eliminate their competition. Since rotting fruit can contain more than 4% of ethanol, animals eating the fruit needed a system to metabolize exogenous ethanol. This was thought to explain the conservation of ethanol active ADH in other species than yeast, though ADH-3 is now known to also have a major role in nitric oxide signaling.
In humans, sequencing of the ADH1B gene (responsible for production of an alcohol dehydrogenase polypeptide) shows two variants, in which there is an SNP (single nucleotide polymorphism) that leads to either a Histidine or an Arginine residue in the enzyme catalyzing the conversion of ethanol into acetaldehyde. In the Histidine variant, the enzyme is much more effective at the aforementioned conversion. The enzyme responsible for the conversion of acetaldehyde to acetate, however, remains unaffected, which leads to differential rates of substrate catalysis and causes a buildup of toxic acetaldehyde, causing cell damage. In humans, various haplotypes arising from this mutation are more concentrated in regions near Eastern China, a region also known for its low alcohol tolerance and dependence.
A study was conducted in order to find a correlation between allelic distribution and alcoholism, and the results suggest that the allelic distribution arose along with rice cultivation in the region between 12,000 and 6,000 years ago. In regions where rice was cultivated, rice was also fermented into ethanol. The results of increased alcohol availability led to alcoholism and abuse by those able to acquire it, resulting in lower reproductive fitness. Those with the variant allele have little tolerance for alcohol, thus lowering chance of dependence and abuse. The hypothesis posits that those individuals with the His variant enzyme were sensitive enough to the effects of alcohol that differential reproductive success arose and the corresponding alleles were passed through the generations.
Classical Darwinian evolution would act to select against the detrimental form of the enzyme (Arg variant) because of the lowered reproductive success of individuals carrying the allele. The result would be a higher frequency of the allele responsible for the His-variant enzyme in regions that had been under selective pressure the longest. The distribution and frequency of the His variant follows the spread of rice cultivation to inland regions of Asia, with higher frequencies of the His variant in regions that have cultivated rice the longest. The geographic distribution of the alleles seems to therefore be a result of natural selection against individuals with lower reproductive success, namely, those who carried the Arg variant allele and were more susceptible to alcoholism.
Mechanism of action in humans
- Binding of the coenzyme NAD+
- Binding of the alcohol substrate by coordination to zinc
- Deprotonation of His-51
- Deprotonation of nicotinamide ribose
- Deprotonation of Thr-48
- Deprotonation of the alcohol
- Hydride transfer from the alkoxide ion to NAD+, leading to NADH and a zinc bound aldehyde or ketone
- Release of the product aldehyde.
The mechanism in yeast and bacteria is the reverse of this reaction. These steps are supported through kinetic studies.
The substrate is coordinated to the zinc and this enzyme has two zinc atoms per subunit. One is the active site, which is involved in catalysis. In the active site, the ligands are Cys-46, Cys-174, His-67, and one water molecule. The other subunit is involved with structure. In this mechanism, the hydride from the alcohol goes to NAD+. Crystal structures indicate that the His-51 deprotonates the nicotinamide ribose, which deprotonates Ser-48. Finally, Ser-48 deprotonates the alcohol, making it an aldehyde. From a mechanistic perspective, if the enzyme adds hydride to the re face of NAD+, the resulting hydrogen is incorporated into the pro-R position. Enzymes that add hydride to the re face are deemed Class A dehydrogenases.
The active site of human ADH1 (PDB:1HSO) consists of a zinc atom, His-67, Cys-174, Cys-46, Thr-48, His-51, Ile-269, Val-292, Ala-317, and Leu-319. In the commonly studied horse liver isoform, Thr-48 is a Ser, and Leu-319 is a Phe. The zinc coordinates the substrate (alcohol). The zinc is coordinated by Cys-46, Cys-174, and His-67. Leu-319, Ala-317, His-51, Ile-269 and Val-292 stabilize NAD+ by forming hydrogen bonds. His-51 and Ile-269 form hydrogen bonds with the alcohols on nicotinamide ribose. Phe-319, Ala-317 and Val-292 form hydrogen bonds with the amide on NAD+.
Structural zinc site
Mammalian alcohol dehydrogenases also have a structural zinc site. This Zn ion plays a structural role and is crucial for protein stability. The structures of the catalytic and structural zinc sites in horse liver alcohol dehydrogenase (HLADH) as revealed in crystallographic structures, which has been studied computationally with quantum chemical as well as with classical molecular dynamics methods. The structural zinc site is composed of four closely spaced cysteine ligands (Cys97, Cys100, Cys103, and Cys111 in the amino acid sequence) positioned in an almost symmetric tetrahedron around the Zn ion. A recent study showed that the interaction between zinc and cysteine is governed by primarily an electrostatic contribution with an additional covalent contribution to the binding.
In humans, ADH exists in multiple forms as a dimer and is encoded by at least seven different genes. There are five classes (I-V) of alcohol dehydrogenase, but the hepatic form that is used primarily in humans is class 1. Class 1 consists of α, β, and γ subunits that are encoded by the genes ADH1A, ADH1B, and ADH1C. The enzyme is present at high levels in the liver and the lining of the stomach. It catalyzes the oxidation of ethanol to acetaldehyde (ethanal):
- CH3CH2OH + NAD+ → CH3CHO + NADH + H+
Another evolutionary purpose may be metabolism of the endogenous alcohol vitamin A (retinol), which generates the hormone retinoic acid, although the function here may be primarily the elimination of toxic levels of retinol.
Yeast and bacteria
Unlike humans, yeast and bacteria (except lactic acid bacteria, and E. coli in certain conditions) do not ferment glucose to lactate. Instead, they ferment it to ethanol and CO2. The overall reaction can be seen below:
- Glucose + 2 ADP + 2 Pi → 2 ethanol + 2 CO2 + 2 ATP + 2 H2O
In yeast and many bacteria, alcohol dehydrogenase plays an important part in fermentation: Pyruvate resulting from glycolysis is converted to acetaldehyde and carbon dioxide, and the acetaldehyde is then reduced to ethanol by an alcohol dehydrogenase called ADH1. The purpose of this latter step is the regeneration of NAD+, so that the energy-generating glycolysis can continue. Humans exploit this process to produce alcoholic beverages, by letting yeast ferment various fruits or grains. It is interesting to note that yeast can produce and consume their own alcohol.
The main alcohol dehydrogenase in yeast is larger than the human one, consisting of four rather than just two subunits. It also contains zinc at its catalytic site. Together with the zinc-containing alcohol dehydrogenases of animals and humans, these enzymes from yeasts and many bacteria form the family of “long-chain”-alcohol dehydrogenases.
Brewer’s yeast also has another alcohol dehydrogenase, ADH2, which evolved out of a duplicate version of the chromosome containing the ADH1 gene. ADH2 is used by the yeast to convert ethanol back into acetaldehyde, and it is expressed only when sugar concentration is low. Having these two enzymes allows yeast to produce alcohol when sugar is plentiful (and this alcohol then kills off competing microbes), and then continue with the oxidation of the alcohol once the sugar, and competition, is gone.
In plants, ADH catalyses the same reaction as in yeast and bacteria to ensure that there is a constant supply of NAD+. Maize has two versions of ADH – ADH1 and ADH2, Arabidopsis thaliana contains only one ADH gene. The structure of Arabidopsis ADH is 47%-conserved, relative to ADH from horse liver. Structurally and functionally important residues, such as the seven residues that provide ligands for the catalytic and noncatalytic zinc atoms, however, are conserved, suggesting that the enzymes have a similar structure. ADH is constitutively expressed at low levels in the roots of young plants grown on agar. If the roots lack oxygen, the expression of ADH increases significantly. Its expression is also increased in response to dehydration, to low temperatures, and to abscisic acid, and it plays an important role in fruit ripening, seedlings development, and pollen development. Differences in the sequences of ADH in different species have been used to create phylogenies showing how closely related different species of plants are. It is an ideal gene to use due to its convenient size (2–3 kb in length with a ~1000 nucleotide coding sequence) and low copy number.
|Iron-containing alcohol dehydrogenase|
bacillus stearothermophilus glycerol dehydrogenase complex with glycerol
A third family of alcohol dehydrogenases, unrelated to the above two, are iron-containing ones. They occur in bacteria and fungi. In comparison to enzymes the above families, these enzymes are oxygen-sensitive. Members of the iron-containing alcohol dehydrogenase family include:
- Saccharomyces cerevisiae alcohol dehydrogenase 4 (gene ADH4)
- Zymomonas mobilis alcohol dehydrogenase 2 (gene adhB)
- Escherichia coli propanediol oxidoreductase EC 126.96.36.199 (gene fucO), an enzyme involved in the metabolism of fucose and which also seems to contain ferrous ion(s).
- Clostridium acetobutylicum NADPH– and NADH-dependent butanol dehydrogenases EC 1.1.1.- (genes adh1, bdhA and bdhB), enzymes that have activity using butanol and ethanol as substrates.
- E. coli adhE, an iron-dependent enzyme that harbours three different activities: alcohol dehydrogenase, acetaldehyde dehydrogenase (acetylating) EC 188.8.131.52 and pyruvate-formate-lyase deactivase.
- Bacterial glycerol dehydrogenase EC 184.108.40.206 (gene gldA or dhaD).
- Clostridium kluyveri NAD-dependent 4-hydroxybutyrate dehydrogenase (4hbd) EC 220.127.116.11
- Citrobacter freundii and Klebsiella pneumoniae 1,3-propanediol dehydrogenase EC 18.104.22.168 (gene dhaT)
- Bacillus methanolicus NAD-dependent methanol dehydrogenase EC 22.214.171.124
- E. coli and Salmonella typhimurium ethanolamine utilization protein eutG.
- E. coli hypothetical protein yiaY.