Lectures 9-11: Orders, inhibition, regulation Flashcards
ternary complex
molecules bound to 2 substrates at the same time
sequential mechanism
involving ternary complex
lineweaver-burk: lines intersect = ternary complex
s1 + s2 available
doesnt tell if random or ordered
pingpong
lineweaver-burk: lines parallel
irreversible inhibitors
react w enzymes
powerful toxins = drugs
reversible inhibitors
penicillin inhibits cell wall
used as drugs t slow down.a soecific enzyme
can bind;
- to the free enzyme and prevent the bindin ofthe substrate
- to the enzyme-substrate complex
competitive inhibition
enzyme is bound to inhibitor = out of circulation
does not effect catalysis
no change in Vmax since can be outcompeted at high conc of substrate
Lineweaver-burk: lines intersect @ same value on yaxis = same value for 1 over Vmax = same Vmax
uncompetitive inhibition
enzyme substrate complex has to form first
free enzyme not affected - doesnt not affect substrate binding but inhibits catallytic function
inhibitor binds to diff region active site no longer functional
decrease in Vmax as inhibitor increases
lineweaver = parallel
mixed inhibition
inhibitor binds regardless of substrate presnce
binds to a regulatory site
inhibits BOTH substrate binding and catalysis
decrease in Vmas
inest intersct left of yaxis
non comp inhibitors are mixes - no change in Km
reversible regulation
modification of enzyme - change activity
covalently- modify enzyme - attach a group to change rate of activity/non covalently - binds near to active site and changes its binding w its sub
covalent changes:
- phosphorylated
- adenylyated - adenine added
acylated - modifying enzymes in DNA packing
- myristeylation -damage repair of proteins
- ubiquitination - marks proteins for degradation
- ADP ribosylation
- methylation
irreversible -
natural inactivated - covenantally i.e enzymes are cleaved to become active
noncovalent: allosteric - reversible regulation:
not bound w a covalent single/double bond - but weak bonds
small molecules: substrates regulators, activators, inhibitors, drugs
bind and can change 3d shape of enzyme
give SIGMOIDAL S-SHAPED MM plot - Vo vs [substrate]
homotropic response- usually to substrate.product
heterotropic - to modulators drugs - makes enzyme move into active enzyme-substrate complex
ATCase - allosteric machine
2 catalytic trimers = 2 active sites
3regulatory dimers
can bind CTP = negative modulator or ATP = +ve modulator = activates the enzyme
inactive Tense state - low activity -
active Relaxed state
substrates = Carbamoyl phosphate and aspartate
early step in pyrimidine synthesis pathway
ARRTCaasw shows a homotropic response to its normal substrate
small increase of substrate = big increase in rate
increasing substrate doesnt = high rate
therefore miz of low and high activity state
identical to haemolobin sigmoidal MM curve
homotropic respnse to substrte
regulatory substrate addition + CTP moves into inactive form - pulls on active site
+ ATP moves towards active relaxed form - opens up structure - reaction goes faster
why is CTP a negative modulator
the pathway is trying to make CTP
high CTP
CTP comes back and binds to regulator dimers - pulls enzyme down into inactive
high ATP = low CTP inducing make more thereofre =ve modulator CTP
non covalent allosteric regulation
feedback inhibition
metabolic pathway converted to isalysin
5 enzyme reaction to make isoleucine
- water removed = threonine dehydralase - inhibited by isoleucine
therefore absence of isoleucine = pathway progresses when little isoleucine appears pathway goes back to beginning
[isoleucine] high enough pathway down regulated
isoleucine levels fall
threonine dehydrase is allosterically resglated by the end prouct of the pathway = isoleucine
pathway becomes self regulating = flux control
blood clotting cascade = irreversible covalent modifivationcascade
polypeptide - factor 11 gets cleaved by active seriene protaees into factor11a - affects next reaction
fibrinogen is activated to become cross-linked
= clot
