Enzyme Kinetics

Question 1

What is kcat?

Answer 1

E is the concentration of enzyme *active site(s) The unit of kcat is 1/sec

Higher the kcat the more powerful the enzyme

Question 2

What is km?

Answer 2

Lower the Km the more efficient the enzyme

Question 3

What is kcat / km?

Answer 3

Catalytic efficiency

Question 4

When can we measure Kcat?

Answer 4

kcat is very specific to the rxn conditions, estimated only when:
✓ the S is bound in the active site
✓ rate is “measured” under saturation conditions
(100% active site filling with S)

Question 5

So what is definition of Kcat?

Answer 5

kcat is the # of substrate molecules converted to products per unit time by a single enzyme (active site) under 100% active site filling conditions

Question 6

What are the units for Kcat?

Answer 6

The unit of kcat is 1/sec

Question 7

What is the definition of Km?

Answer 7

Km is the [S] where the reaction has achieved ½ Vmax
(i.e. 50% of the enzyme active sites are filled with substrate).

Question 8

What does Km stand for?

Answer 8

Michaelis Constant

Question 9

Which Enzyme is more Efficient?

Answer 9

E1 is more efficient than E2
as it achieves same ½ Vmax at a Lower [S]