Lecture 12: HOW FAST IS THAT ENZYME? Flashcards
What is shown on the lineweaver-burk plot?
The double reciprocal of the michaelis-menten equation: 1/v=km/vmax x 1/[S] +1/vmax
What is on the x axis of the lineweaver burk plot?
1/[S]
What is on the y axis of the lineweaver burk plot?
1/vo
What is the slope of the lineweaver-burk plot?
km/Vmax
What is the x intercept of the lineweaver-burk plot?
-1/Km
What is the y-intercept of the lineweaver-burk plot?
1/vmax
What does km characterise?
One enzyme-substrate pair (if an enzyme can act on different substrates, it will have different Km values for each
What is the Km?
The [S] needed to reach half of vmax
What are the units of Km?
The units of concentration (mmol/L)
What is Km formally?
k-1 +k2 /k1
How do k2 and k-1 compare in many enzymes?
k2«
What is the more useful equation for Km?
k-1/k1 (the ES dissociation constant)
What does a low km mean?
High affinity between E and S
What does a high Km mean?
A low affinity between E and S
How is the [S] in a cell for a particular enzyme-substrate interaction?
Often below the Km
What does [S] being below Km in a cell mean?
Rate will rise to accommodate more substrate, tending to maintain steady state
What does hexokinase do?
Generates energy in muscle and brain (wants to use it straight away)
What is hexokinase Km for ATP?
0.04mM
What is hexokinase Km for glucose?
0.05mM
What is an isozyme of hexokinase?
Glucokinase
What does glucokinase do?
Store energy as glycogen in the liver (not used straight away)
What is the km of glucokinase for glucose?
6mM
What is the Km for each isozyme and substrate?
Different
What are the classes of inhibitor?
Irreversible and reversible (competitive or noncompetitive- pure or mixed)
How do irreversible inhibitors bind?
Covalently to the enzyme