Chapter 5 (Part 1)
1) Define Catalyst and know the properties of a catalyst.
2) Know the 6 classes of enzymes and there functions. Be able to classify a specific
enzyme if given the reaction.
3) Define Coenzyme, apoenzyme, holoenzyme,
Chapter 5 (Part 2)
1) Define rate constant, first order reaction, second order reaction and zero order
reaction
2) Define Vmax
3) Define Km
a) Km = the substrate concentration at ½ Vmax
b) Km = (k-1+Kcat)/k1
c) X-intercept on a Lineweaver-Burk plot
4) Michaelis-Menton equation defines the hyperbolic curve when [S] is plotted
against initial velocity
5) Know what the initial velocity and steady state assumptions mean.
a) Initial velocity assumption – assumes that at initial velocity so little product
is formed that the back conversion of product to the ES complex (P->ES)
is negligible and the k-2 is zero.
b) Steady state assumption – the rate of ES complex formation = the rate of
ES complex breakdown. Therefore at steady state the concentration of ES
complex is constant.
6) Km is usually higher than the physiological [S]. Allows enzyme to respond rapidly
to changes in metabolism.
7) Know the relationship between Km and substrate binding to the enzyme. High Km
= weak binding. Small Km = tight binding.
8) Kcat.
a) kcat is the 1st order rate constant describing ES -> E+P.
b) Also known as the turnover # because it describes the number of rxns a
molecule of enzyme can catalyze per second under optimal condition.
c) Most enzyme have kcat values between 102 and 103 s-1
d) For simple reactions k2 = kcat , for multistep rxns kcat = rate limiting
step
d) Vmax = Kcat [Total Enzyme]
9) Kcat/Km
a) It measures how the enzyme performs when S is low
b) kcat/Km describes an enzymes preference for different substrates =
specificity constant
c) The upper limit for kcat/Km is the diffusion limit - the rate at which E
and S diffuse together (108 to 109 m-1 s-1)
d) Catalytic perfection when kcat/Km = diffusion rate
10) Limitations of Michaelis-Menton
a) Some enzyme catalyzed rxns show more complex behavior E + S<>ES<->EZ<->EP<-> E + P With M-M can look only at rate limiting step
b) Often more than one substrate E+S1<->ES1+S2<->ES1S2<->EP1P2<> EP2+P1<-> E+P2
Must optimize one substrate then calculate kinetic parameters for the other
c) Assumes k-2 = 0
d) Assumes steady state conditions
Chapter 5 (part 3)
1) Lineweaver Burk plots
a)Plot 1/[S] vs 1/Vo
b) L-B equation for straight line
c)X-intercept = -1/Km
d) Y-intercept = 1/Vmax
e) Easier to extrapolate values w/ straight line vs hyperbolic curve
f) 1/Vo = (Km/Vmax)(1/[S]) + 1/Vmax
2) Mutlisubstrate Reactions
a) Know how to read and write Cleland Notations for
i) Sequential rxns (ordered and random)
ii) Ping-Pong rxns
b) Understand the general properties of each type of reaction.
c) If given a Lineweaver Burk plot of a multisubstrate reaction, be able to
determine whether the rxn is sequential or Ping-Pong
3) Inhibitor kinetics
a) know the general properties of competitive, uncompetitive, and noncompetitive inhibitors
b) know how each type of inhibitor interacts with an enzyme.
c) Know how each type of inhibitor affects Km and Vmax
d) Know how the addition of each type of inhibitor effects how the data looks
on a Lineweaver Burk plot.
4) Irreversible inhibitors – know the differences between a reversible and irreversible
inhibitor.
Chapter 5 (part 4)
1) Allosteric regulation
a) Define allosteric activator, allosteric inhibitor,
b) Know that an allosteric modulator binds to site other than active site
c) Allosteric enzymes usually have quaternary structure.
d) [S] vs Vo plots are sigmoidal for at least one substrate(i.e. don’t have
Michaelis Menton Kinetics)
e) For some enzymes (phosphofructokinase), addition of allosteric
modulators effect Km (substrate binding). For other enzymes, addition of
allosteric modulators effect Vmax.
f) Can remove allosteric domain without affecting catalytic domain.
g) Allosteric transition from T (tense) to R (relaxed) conformation can
proceed by two models. 1) concerted model – binding of allosteric
modulator converts all subunits to R form or 2) Sequential model –
allosteric modulator must bind to each subunit before that subunit can
convert to R form.
h) End products of a biosynthetic pathway often function function as allosteric
inhibitors of a rate determining enzyme
2) Covalent Modification
a) Slower means of regulation than allosteric modification.
b) Reversible
c) Involves two additional enzymes 1) one to modify target enzyme and 2)
one to convert the modified target enzyme to the original state
d) Covalent modification could cause either activation or inactivation of
enzyme activity (depends on the enzyme).
e) Covalent modification “freezes” enzyme in T or R conformation.
f) Phosphorylation/dephosphorylation is good example
3) Regulation of enzyme activity by subunit association/disassociation
a) know that subunit association can either activate enzyme or inactivate
enzyme depending on specific case.
b) Association/disassociation could be modulated by the pathway precursors
or pathway products
4) Regulation by proteolytic cleavage of proenzyme
a) Define zymogen