Lecture 3.3: Enzyme Kinetics

Question 1

What are michaelis menten assumptions

Answer 1

1. no appreciable enzyme-product complex (EP) is formed, so the back of EP to ES is negligible
2. the release of P from E is fast so the backward step to form ES from E + P is negligible
3. The reaction is measured under steady-state conditions –> [ES] remains constant

Question 2

For an enzyme to convert a substrate to a product:

Answer 2

1. an enzyme-substrate complex [ES] must be first formed
2. the chemistry occurs to convert substrate to product and finally product is released

Question 3

Michaelis Constant (Km)

Answer 3

Km = k-1 +k2/ k1

Question 4

Km trends

Answer 4

increased Km = decreased affinity for enzyme
decreased Km = increased substrate affinity = high catalytic active at low [S]

Question 5

Vmax

Answer 5

maximum velocity that occurs when the enzyme is fully saturated

Vmax = k2 [Et]

Question 6

Km is [ ] of enzyme concentration [E]

Answer 6

independent

Km is dependent on interactions between substrates

Question 7

Turnover number

Answer 7

the number of conversions of susbtrate to product per unit time for one enzyme at saturation (at Vmax)

Kcat = Vmax/[Et]

Question 8

Specificity constant

Answer 8

• the specificity constant depends on affinity of the enzyme for a given substrate and the rate of catalysis with the substrate
• if Kcat = big and Km = small increase catalytic efficency
• Kcat/Km

Question 9

Limit of diffusion

Answer 9

10^8 - 10^9 M^-1 sec^-1