Lecture 8 - Enzyme Kinetics Flashcards
(16 cards)
What do oxidoreductases do
Catalyse redox reactions
Transfer of hydrogen and oxygen atoms from one substrate to another
eg. Alcohol dehydrogenase oxidises alcohols
What do transferases do
Catalyse the transfer of functional groups from one compound to another
eg. hexokinase
What do hydrolase do
Catalyse the hydrolytic cleavage of C-O, C-N and C-C bonds
eg. carboxypeptidase A
What do lyases do
Catalyse the cleavage of C-C, C-O and C-N bonds by elimination (not hydrolysis)
Conversely, catalyse the addition of groups to double bonds
eg. pyruvate decarboxylase
What do isomerases do
Catalyse geometric or structural changes within one molecule (isomerization)
Conversely, catalyse the addition of groups to double bonds
eg. maleate isomerase
When does V0 occur
initial rate of catalysis
number of moles of product formed per second at the start of the reaction
What does the Michaelis menten equation link
enzyme rate of reaction to substrate concentration
What is a pre steady state
When the enzyme is first mixed with a large excess of substrate (initial transient state) during which the concentration of ES builds up
This state is usually too short to observe
(often microseconds)
What is steady state
[ES] remains approximately constant
What is the Michaelis-menten model equation
[ES] = [E][S] / KM
(slide 17)
What do variations in KM mean
Enzymes have different KM values for different substrates
Different enzymes will have different KM values for the same substrate
The lower the KM the better the enzyme can process the substrate
How does KM value show enzyme characteristics
A high KM indicates weak binding
A low KM indicates strong binding
KM provides a measure of the [S] required for significant catalysis to take place
What does Vmax show about an enzyem
reveals the turnover number of an enzyme
What is the turnover number of an enzyme
the number of substrate molecules converted into product by an enzyme molecule in a unit time when the enzyme is fully saturated with substrate
How can Kcat/KM measure catalytic efficiency
When [S]»_space; KM, the rate of catalysis is equal to Vmax, which is a function of kcat
What is a line waver-burk plot
provides a straight-line with a y-intercept of 1/Vmax and a slope of KM/Vmax. The intercept on the x-axis is -1/KM
