Enzyme Kinetics and Inhibition 10/4 Flashcards
characteristics of enzymes
- cataylze chemical reactions without being consumed 2. very selective 3. products of natural selection
delta G less than 0
spontaneous reaction
delta G greater than 0
non-spontaneous reaction
enzyme catalysis reaction
E+S →[ES]→E+P
active site
has a shape that accomodates and complements the subtrate, including polarity and charge complentarily to the substrate transition state
to be an effective catalyst, should the enzyme bind tighter to the substrate or to the transition state?
the transition state! **this makes TS analogs good inhibitors of enzyme (for drugs)
kcat
the rate at which the ES complex converts to free enzyme and product. units: s-1
Km
the dissociation constant for the enzyme substrate complex. units=M
Vmax
the maximal value for an enzyme reaction
rate saturation equation
[E]0=[E]+{ES]
when [S] is low, the enzyme is mostly ________. how does v increase?
[E]
v increases proportionally to [S]
when [S] is high, the enzyme is mostly _____. how does v increase?
[ES]
v increases slowly in proportion to [S]
steady state enzyme kinetics equation
v=(Vmax[S])/Km+[S]
the upper limit of the forward reaction is
Kcat
carbonic anhydrase
catalyzes interconversion of carbon dioxide and bicarbonate
reversible inhibitor I
binds and dissociates from an enzyme; doesn’t react, just prevents substrates from reacting
irreversible inhibitor
binds to and permanently inactivates an enzyme
how does aspirin affect COX (cyclooxygenase)?
aspirin inactivates cox enzymes (cox synthesize prostaglandins, causing inflammation) - aspirin PERMANENTLY acetylates the active site serine residue. this slows blood clotting
aspirin toxicity
- salicylate (the remainder of the aspirin molecule ones it inactivates COX) binds to other proteins causing tinnitus (ear ringing) - can result in SATURATION of liver enzymes
- anion gap metabolic acidosis - interrupts aerobic respiration, leading to anaerobic production of lactate
for reversible enzyme inhibitors, the amount of inhibition depends on:
the concentration of the inhibitor [I]
competitive inhibitors prevent substrates from binding to…
the free enzyme. normally binds to the enzyme’s ACTIVE SITE
noncompetitive inhibitor
has no effect on substarte binding - prevents reaction of the bound substrate
dihydrofolate reductase (DHFR)
enzyme that is used to make DNA
what does methotrexate inhibit?
DHFR - used in leukemia (acute lymphoblastic leukemia) treatments. is COMPETITIVE inhibitor
there are 5 ways that enzymes can be regulated. they are:
- substrate/cofactor availability
- product inhibition
- allosteric activation and inhibition
- positive and negative cooperativity
- post-translational modification
negative feedback
the product inhibtis the process from happening again
glucose-6-P is catalyzed by:
glucokinase and hexokinase
the Km for glucose is higher in ______ than _______. why is this important?
Km is higher in glucokinase (10mM) than hexokinase (0.1 mM). This means that hexokinase has a high affinity for the substrate
allosteric regulation of an enzyme occurs where? what type of inhibitors do this?
at a site on the enzyme OTHER that the active site. noncompetitive inhibitors are allosteric inhibitors.
thrombin
a blood clotting factor. has 2 confirmations:
- slow: an anticoagulent (cleaves protein C, a clotting inhibitor)
- fast form: cleaves fibrinogen; coagulent
conversion between the slow and fast forms is ALLOSTERICALLY REGULATED by the binding of Na+
amount of slow/fast thrombin in the blood?
serum thrombin is 60%fast/40%slow
what type of curve does positive cooperativity give?
sigmoid curve - means that v is less responsive at low [S]
glycogen phosphorylase
enzyme that converts glycogen to glucose-1-P. exists in 2 forms.
- b (native form), T (tense) state - has a high Km, or poor substrate affinity (would want to DISSOCIATE)
- a form favors R (relaxed) state, has low Km, meaning it has high substrate affinity
(a phosphorylase converts the a form back to the b form)
AMP is a(n) ____________ activator
allosteric
what is a zymogen?
an inactive precursor that is turned on by proteolytic cleavage, many pancreatic/digestive enzymes are this
