Lock-and-Key Model (Emil Fischer, 1894):

• Enzyme = lock (has a specifically shaped active site)
• Substrate = key (specific 3D shape complementary to active site)
• Only the correct substrate fits precisely into the active site
• This specificity ensures each enzyme catalyzes only specific reactions

Michaelis-Menten Kinetic Steps:

1. Enzyme (E) + Substrate (S) ⇌ Enzyme-Substrate complex (ES) [fast, reversible]
2. ES → Enzyme (E) + Product (P) [slow, rate-determining step]

$E + S \underset{k_{-1}}{\overset{k_1}{\rightleftharpoons}} ES \overset{k_2}{\rightarrow} E + P$

$K_m = \frac{k_{-1} + k_2}{k_1}$

Characteristics of Enzyme Catalysis:

• High specificity: Follows lock-and-key mechanism; each enzyme acts on specific substrate(s)
• Optimal conditions: Maximum activity at specific pH (body enzymes ~7.4) and temperature (~37°C for human enzymes)
• Denaturation: At extreme pH or temperature, enzyme conformation changes → active site shape lost → loss of activity
• Saturation kinetics: At [S] >> Km, enzyme is fully saturated; rate = Vmax (zero-order kinetics)

Types of Inhibition: