Enzyme kinetics #2 Flashcards
Lineweaver-Burk plot shows increasing inhibition by…
the lines getting flatter/lower
Michaelis-Menten graph shows increasing inhibition by…
the lines getting steeper
EI
reduces the effective free [E] available for S binding
Competitive inhibition
normal graph shows
alpha is
a function of [I] - modulations Km
no inhibitor, alpha =
1
Lineweaver-Burk plot shows uncompetitive inhibition by…
parallel lines
Lineweaver-Burk plot shows non-competitive inhibition by…
lines have the same Km so all cross the X axis at the same place
Uncompetitive inhibition
~ rare
~ inhibitor can only bind ES complex
~ both Km and Vmax change
Non-competitive inhibition
~ inhibitor binds enzyme irrespective of whether substrate is bound or not
~ V max changes
~ Km stays the same
Initial velocity
V0
~ function of increasing substrate concentration
~ measured for Michaelis-Menten kinetics
What is plotted in Lineweaver-Burk
plotting reciprocals of V0 against [S]
Catalytic efficiency is measured using
Vmax and Km
What are the three possible mechanisms for multiple substrates + products (bi-bi)
~ ordered
~ random
~ ping-pong
Ordered bi-bi
E + A –> EA + B –> EAB –> EPQ –> EQ + P –> E + Q
~ some NAD+/NADP+-requiring enzymes
Random bi-bi
~ similar to ordered but A or B can be added first and then P or Q can leave first (no order preference)
~ some dehydrogenases and kinases
Ping-pong
E + A -> EA-FP –> F + P –> F + B –> FB-EQ –> E + Q
~ chymotrypsin, flavoproteins, transaminases
How can bisubtrate mechanisms be differentiated? - PING-PONG
~ Lineweaver-Burk
~ double reciprocal plot = parallel lines when altering one substrate conc.
How can bisubtrate mechanisms be differentiated? - SEQUENTIAL/ORDERED
~ Lineweaver-Burk
~ double reciprocal plot
~ multiple lines have the same Km value
~ random gives similar outcome
How do increasing concentrations of substrates/constants in bisubstrtae mechanisms effect the graph?
the lines on Lineweaver-Burk become shallower, the more the constant (A or B) increases
