Bisubstrate reactions

Question 1

How many enzymes have 2 substrates?

Answer 1

60%

Question 2

What are the two mechanisms of bisubstrate reactions catalyzed by enzymes?

Answer 2

Ternary complex and ping pong

Question 3

How does the ternary complex mechanism work?

Answer 3

Both substrates bind at the same time then the reaction proceeds through the ternary complex

Question 4

How does the ping pong mechanism work?

Answer 4

One substrate binds, reacts and modifies the enzyme, then the second substrate binds and reacts and regenerates the original enzyme

Question 5

How do you differentiate between the ternary complex and ping pong mechanism?

Answer 5

Different kinetics when you plot the reaction rate vs a range of substrate 1 concentrations, then test a range of substrate 2 concentrations

Question 6

What pattern is seen in the kinetics of a reaction with the ternary complex mechanism?

Answer 6

Resembles the Dixon plot of a mixed inhibitor

Question 7

What pattern is seen in the kinetics of a reaction with the ping pong mechanism?

Answer 7

Resembles the Dixon plot of an uncompetitive inhibitor

Question 8

What type of reaction mechanism does DNA kinase use?

Answer 8

Ternary complex. Both DNA and ATP bind in the active site and react

Question 9

What type of reaction mechanism does DNA phosphatase use?

Answer 9

Ping pong. The enzyme reacts with DNA, binds covalently to it, then water cleaves that bond and regenerates the enzyme