CHEM 3521 - Exam 2

Michaelis-Menten equation

V₀ = (V_max [S]) / (K_M + [S])

V₀

Initial velocity

V_max

Maximum velocity (when all enzyme is bound to substrate)

• K₂ [E]

K_M

Michaelis constant: measure of substrate/enzyme binding affinity

• [S] at which the reaction is at ½ V_max

• (K _-1 + K₂ ) / K₁

K_cat

Turnover number

• [S] converted to product per active site per second - reflects the slowest step

• V_max / [E]_T

K_cat / K_M

Catalytic efficiency

• K_cat / K_M

What does low K_M mean about affinity?

High substrate affinity because less [S] is needed to bind more enzyme

What happens to V₀ when [S] = K_M

V₀ = ½ V_max

What happens to V₀ when [S] > > K_M

V₀ = V_max

Competitive Inhibition

• What is it?

• What happens to K_M and V_max

Inhibitor competes directly with the substrate for the enzyme active site

• K_M Increases

• V_max is Unchanged

Un-competitive Inhibition

• What is it?

• What happens to K_M and V_max

Binds after the ES complex is made (substrate bound to enzyme) and inhibits

• K_M decreases

• V_max decreases

Non-competitive Inhibition

• What is it?

• What happens to K_M and V_max

Inhibitor binds to allosteric site on enzyme that prevents the substrate from binding

• K_M is unchanged

• V_max decreases