Lectures 11-12 Flashcards
Reaction types:
Isomerization
Condensation/Lysis
Complicated
Reaction rate equation:
V = -Δ[S] / Δt V = +Δ[P] / Δt
How quickly should V0 be measured?
Before 10% of reactant is used up; before a reverse reaction has the chance to begin.
Rate limitations:
E + S -> ES -> (EP ->) E + P
Can be limited by substrate, at transition to ES.
Can be limited at transition to product.
ES -> EP usually takes the same amount of time every time; EP -> E + P is very fast.
Michaelis-Menton equation:
V0 = ([S] * Vmax) / ([S] + Km)
Km is often near the physiological concentration of substrate of target cell.
Glycolysis and Km:
Hexokinase (in all cells) initiates glycolysis. Km = 30 uM.
Glucokinase (in brain, liver, pancreas) is a glucose concentration sensor. Km = 10 mM.
They perform the same reaction at different Kms.
Asian glow:
Alcohol dehydrogenase (ADH) and acetaldehyde dehydrogenase (ALDH) break down [ethanol -> acetaldehyde -> acetic acid] by NAD+ -> NADH. ALDH1 (cytoplasm) causes bad symptoms, so you want to break it down as quickly as possible. ALDH2 (mitochondria) is okay. ALDH1 has a high Km so it doesn't work properly until you're at a v high concentration of acetaldehyde, which is bad. 50% of asians have a mutation in ALDH2, raising its Km, so the body has to wait until acetaldehyde concentration is unfortunately high for ALDH1 to kick in.
kcat equation:
kcat = Vmax / [E]t ***?
L-B plot - what things mean what?
x-int: -1/Km
y-int: 1/Vmax
x-axis: 1/[S]
y-axis: 1/V0
Mechanisms of inhibition:
Competitive: binds active site.
Uncompetitive: binds ES complex and slows P release.
Noncompetitive: binds enzyme.
Competitive inhibition:
Vmax stays the same but requires higher [S].
Km goes up.
Moonshine and inhibition:
Methanol is REALLY BAD FOR YOU.
Methanol’s Km = 130 mM
Ethanol’s Km = 20 mM
Graph shape: *
Uncompetitive inhibition:
Vmax goes down.
Km goes down - not a lot of free E, lots of ES.
Think about equilibrium.
Graph shape: ///. (un = up)
Noncompetitive inhibition:
Pacman closes its mouth. Slight conformation change in shape of active site of E.
Vmax goes down - [S] has no effect.
Km stays the same.
Shape: rotate about Km.
The difficulties of enzyme standardization:
Different enzymes complete different reactions. Enzymes that complete the same reactions may have different Vmax or Km. A sample may be affected by purity, source organism.
