Alcohol / Ethanol / Booze

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Alcohol / Ethanol / Booze
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Making Alcohol

• The enzyme alcohol dehydrogenase plays a central
  role in the most ancient form of biotechnology
  alcoholic fermentation.
• Yeast and many bacteria produce alcohol
  dehydrogenases. These microbial enzymes catalyze
  the last step in the conversion of food into
  metabolic energy, creating ethanol.
• Sugars are broken down and used for energy,
  forming ethanol as the waste product, which is
  excreted into the liquid surrounding the cell.
• We have harnessed this process to produce
  alcoholic beverages yeast is allowed to ferment
  grain sugars to form beer, and yeast is allowed
  to ferment grape juice to form wine.

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• Microbial ADH
• Tetramer
• 4 x 352 amino acid residues
• 4 zinc ions (Zn)
• 4 NAD cofactors

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Making Alcohol

• Alcohol dehydrogenases in microbes function as
  tetramers.
• They are zinc-containing enzymes that utilize
  glucose.
• Each glucose molecule is broken down in a
  10-step process called glycolysis. The product
  of glycolysis is two three-carbon sugars, called
  pyruvates, and ATP (adenosine triphosphate).
• The two pyruvates are then converted into
  ethanol and carbon dioxide.

The overall process of fermentation is to
convert glucose sugar to alcohol and carbon
dioxide gas C6H12O6     ?   2 CH3CH2OH     
         2 CO2    sugar  
  alcohol         
   carbon dioxide gas (glucose)
   (ethyl alcohol or ethanol)
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Making Alcohol

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Making Alcohol

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Breaking Down Alcohol
In 1997, Americans drank an average of 2 gallons
(7.6 liters) of alcohol per person. This
translates roughly into one six-pack of beer, two
glasses of wine and three or four mixed drinks
per wee. So while recovering from the excesses
at the Anthill Pub last night after it reopens
next fall, we might ponder the human alcohol
dehydrogenase enzyme, which ceaselessly battles
all the beer wine that we have consumed.
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Breaking Down Alcohol

• Alcohol dehydrogenase is our primary defense
  against alcohol, a toxic molecule that
  compromises the function of our nervous system.
• The high levels of alcohol dehydrogenase in our
  liver and stomach detoxify about one drink each
  hour.
• The alcohol is converted to acetaldehyde, an
  even more toxic molecule and the main cause of
  hangovers!
• Acetaldehyde in turn is converted to acetate and
  other molecules that are easily processed by our
  cells.

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• Human ADH
• Homodimer (two molecules)
• 2 x 373 amino acid residues
• 6 zinc ions (Zn)
• 2 NAD cofactors

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Human ADH Microbial
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Breaking Down Alcohol

Alcohol dehydrogenase
CH3CH2OH     2 NAD   ? CH3CHO    
2 NADH alcohol         
cofactor  aldehyde
cofactor (ethanol)
(acetaldehyde)

Acetaldehyde dehydrogenase 2 CH3CHO
H2O   ? CH3COOH   aldehyde

acid (acetaldehyde)
(acetic acid or vinegar)
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Breaking Down Alcohol

Acetaldehyde dehydrogenase 2 CH3CHO
H2O   ? CH3COOH   aldehyde

acid (acetaldehyde)
(acetic acid or vinegar)
The acetic acid can be used to form fatty acids
(watch that waistline!), or it can be further
broken down into CO2 and water.
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Dangers of Alcohol

• Alcohol dehydrogenase provides a line of defense
  against a common toxin in our environment.
• But alcohol dehydrogenase also modifies other
  alcohols, sometimes producing even more dangerous
  products
• Methanol, which is commonly used to denature
  ethanol rendering it undrinkable, is converted to
  formaldehyde by alcohol dehydrogenase.
• The formaldehyde then causes severe damage,
  attacking proteins and embalming them.
• Small amounts of methanol cause blindness, as
  the sensitive proteins in the retina are
  attacked, and larger amounts, perhaps a glassful,
  lead to widespread damage and death.

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Breaking Down Methanol

Alcohol dehydrogenase
CH3CH2OH     2 NAD   ? CH3CHO    
2 NADH alcohol         
cofactor  aldehyde
cofactor (ethanol)
(acetaldehyde)

Alcohol dehydrogenase CH3OH 
    2 NAD   ? CH3CHO     2 NADH
alcohol    cofactor
 aldehyde cofactor
(methanol)
(formaldehyde)
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Structure (Form) Function

• Our bodies create at least nine different forms
  of alcohol dehydrogenase, each with slightly
  different properties.
• Most of these are found primarily in the liver,
  including the b3 form
• The s form is found in the lining of the
  stomach.
• Each enzyme is composed of two subunits.
• Ethanol is not the only target or substrate of
  these enzymes, they also make important
  modifications to retinol, steroids, and fatty
  acids.

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Structure (Form) Function

• Human alcohol dehydrogenases use two helpers
  to perform their reaction on ethanol.
• The first are zinc ions (Zn), which are used
  to hold and position the alcohol group on
  ethanol.
• The second is the NAD cofactor (constructed
  using the vitamin niacin), which actually
  performs the chemical reaction.
• The zinc atom, shown in light blue, is cradled
  by three amino acids from the protein cysteine
  46 to the left, cysteine 174 to the right, and
  histidine 67 above. The ethanol, shown in green
  and magenta, binds to the zinc and is positioned
  next to the NAD cofactor, which extends below the
  ethanol molecule in this illustration.