W28 L1 - Enzyme Mechanisms with Two Substrates

Flashcards about enzyme mechanisms with two substrates, including ordered ternary complex, random ternary complex, and ping pong mechanism.

What are the two substrates called in the reaction of pyruvate to lactate?

Pyruvate and NADH.

In enzyme reactions with two substrates, what does the scheme E + A + B -> products represent?

A simplified representation of an enzymatic reaction involving two substrates (A and B) forming products.

What is an ordered ternary complex?

A reaction mechanism where the substrates must bind to the enzyme in a specific order.

In Cleland's notation for an ordered ternary complex, what does EAB represent?

The enzyme with both substrates A and B bound.

What does 'Bi Bi' refer to in enzyme kinetics?

A reaction involving two substrates and two products.

What is a Cleland plot?

A shorthand notation depicting the order of substrate binding and product release in enzyme reactions.

What is a random ternary complex?

A reaction mechanism where the order of substrate binding to the enzyme does not matter/ makes no difference.

In a Cleland plot, how is a random ternary complex depicted?

Showing multiple pathways where either substrate A or B can bind first.

What is a ping pong mechanism?

A reaction mechanism where one substrate binds and releases a product before the second substrate binds.

Does a ping pong mechanism have a ternary complex?

No, a ping pong mechanism does not have a ternary complex.

How can you experimentally distinguish between ternary complex and ping pong mechanisms?

By adding the first substrate and observing if a product is formed without the addition of the second substrate (ping pong), and by the presence or absence of modified enzyme species.

In terms of identifying the reaction mechanism, what does isolating an intermediate indicate?

Isolating an intermediate during a reaction typically suggests a ping-pong mechanism.

• A ping-pong mechanism involves at least two steps. In the first step, the enzyme is modified (a group is transferred from the first substrate to the enzyme) and then restored to its original form in the second step (the group is transferred from the enzyme to the second substrate).

• The ability to isolate the modified enzyme intermediate provides strong evidence for this type of two-step or multi-step mechanism.

In terms of identifying the reaction mechanism, what does the inability to isolate an intermediate indicate?

It does not necessarily mean a ternary complex since the equipment might just be insufficient, for example.

How do you identify a Ping Pong mechanism by using a Lineweaver-Burk plot?

The lines are parallel.

In a Lineweaver-Burk plot, what is a characteristic of a ternary complex?

The lines are not parallel but intersect.

In a ping pong mechanism, how is the concentration of product P related to the enzyme concentration?

The concentration of P is equal to the concentration of the modified enzyme.

Can the three mechanisms mix with each other?

Random and Ordered can mix with each other. There is no known mixture between Ping Pong and Ternary.

Which two-substrate enzyme will be investigated in the practical session?

Lactate dehydrogenase.

what is a ternary complex?

A ternary complex is formed when an enzyme binds to two substrates simultaneously, creating an intermediate that facilitates the reaction between them.