Enzyme - controlling rates - regulating and inhibiting Flashcards
effect of temp on V
increase temp - add heat energy - easier to reach Ae
speed molecule increase therefore collide more per second
opt 37-40 over - decreases rate because denature - unravel protein E
effect of pH on V
e.g. lysozyme - pH7
pepsin - acidic
alkaline phosphatase - alkaline
denature above/below opt pH
effect [E] on V
[S] - constant
V = (Vmax*[S]) / (Km+[S])
increase in [E] = increase Vmax = increase V
enzyme regulation
covalent
non-covalent
covalent - enzyme regulation
break/make covalent bond - alter activity of enzyme - change bond
irreversible process
covalent - zymogen
cleave peptide chain - made in cell and released - turn full mature E = active
covalent - zymogen - example
digestive enzyme in gut - convert zymogen in gut
covalent - reversible process
phosphorylation - on and off
phosphorylation - covalent
phosphate -ve therefore bind to side chain = repel/attract groups = distortion
reverse - use phosphatase - return to original shape
non-covalent - enzyme regulation
reversible binding of molecules of specific site
increase/decrease activity
regulation can be at binding/catalysis steps or both
enzyme regulation - equations
E + S <> ES -> E + P
E + S <> ES
K type - B
ES -> E + P
V type - C
cooperativity (K-type regulation)
S binding to one side - increase affinity at another binding site
cooperativity examples -
2 enzymes = dimer act as regulator of each other
start at low affinity and when S binds - affects propagate
most S not affect - [S] regulate E activity - independent to [S] = increase V
M-M kinetics
Michaelis-Menten kinetics
non-M-M kinetics
sigmoidal curve
1/2 Vmax - K0.5 for non-M-M kinetics
sigmoidal curve
multiple subunit E with cooperative changes in S affinity between subunit - decrease activity due to decrease [S]
allosteric enzyme (K-type)
regulated by binding to another molecules not S - completely different
allosteric activator
low affinity - no bind at active site
high affinity - caused by another molecule on regulatory subunit
allosteric inhibitor
low affinity - molecule bind to regulatory subunit
high affinity - no binding
allosteric enzyme - Km
altered easily by changing conc of allosteric molecule
allosteric enzyme (V-type)
less common
effect catalytic step - speed not binding
Vmax changes depending on V type allosteric enzyme conc
while all will have same K0.5
unwanted regulation
all through allosteric E - set up to be regulated by changing level of molecules
unwanted regulation - in cell - principle
molecules that naturally vary therefore enzyme matched to changing levels of natural molecules
unwanted regulation - decrease activity
molecules outside body has nothing to do with body - can bind to E and change activity
enzyme inhibitor
decrease decrease E activity - irreversible/reversible - decrease V and compared to absence of molecule - might resemble S or different
various different forms = different
irreversible inhibitor
suicide S
e.g. aspirin
penicillin
aspirin
close to S - binds at active site and starts to catalysis
never finishes therefore permanent covalent alteration of enzyme
penicillin
bond breaks and attaches to end to active site - block
stop bacteria from building cell wall
therefore E is no longer functional therefore must move more E for reaction to occur
reversible inhibitor
competitive
non-competitive
uncompetitive
mixed
competitive inhibitor
loss of binding process - similar shape to S bind to active site and block
bind somewhere else - distort active site therefore cannot bind
Vmax stays same and V decreases
Km - larger (poor binding) as if [S] was less
equation of competitive inhibitor
V = (Vmax[S]) / (KmIf)+[S]
where If is at E + S - decreases V
If
inhibition factor
= I + [I]/Ki
non-competitive inhibitor
loss of catalysis process - prevent reaction when E binds to S
Vmax is smaller
Km is same and 1/2 Vmax is changed
as if [E] was less
equation of non-competitive inhibitor
V = (Vmax/If)[S] / (Km+[S])
where If is at E+S (EI) and ES(ESI) - decreases V
uncompetitive inhibitor
bother Vmax and Km seem smaller
forces E to hold onto S even if reaction doesn’t occur
equation of uncompetitive inhibitor
V = (Vmax[S]) / Km+([S]If)
where If is at ES(ESI)
mixed inhibitor
bind to either but with different affinity of E and ES
line crosses but not at the axis - on graph
