Subtopic: Nature of Enzyme action

Enzyme-Substrate Interaction

• Speci­fici­ty: Each enzyme (E) has a spe­cif­ic sub­strate (S) bind­ing site with­in its struc­ture.
• Enzyme-Sub­strate Com­plex (ES): The bind­ing site facil­i­tates the for­ma­tion of a high­ly reac­tive, tran­sient (short-lived) ES com­plex.
• Enzyme-Prod­uct Com­plex (EP): The ES com­plex tran­si­tions into an EP com­plex.
• Prod­uct For­ma­tion and Enzyme Regen­er­a­tion: The EP com­plex dis­so­ci­ates, yield­ing the product(s) ℗ and regen­er­at­ing the unchanged enzyme (E).
• Over­all Reac­tion: E + S ⇌ ES → EP → E + P
• Impor­tance of ES For­ma­tion: Cru­cial for the cat­alyt­ic activ­i­ty of the enzyme.

Catalytic Cycle of Enzyme Action (Step-by-Step)

• 1. Sub­strate Bind­ing:
  • The sub­strate mol­e­cule encoun­ters the enzyme.
  • The sub­strate fits specif­i­cal­ly into the enzyme’s active site.
  • Two mod­els explain this inter­ac­tion:
    • Lock and Key Mod­el: The sub­strate per­fect­ly fits the pre-exist­ing active site of the enzyme, like a key in a lock.
    • Induced Fit Mod­el: Sub­strate bind­ing trig­gers a con­for­ma­tion­al change in the enzyme’s shape, allow­ing the enzyme to snug­ly fit around the sub­strate, max­i­miz­ing inter­ac­tion and sta­bi­liz­ing the tran­si­tion state. This is the cur­rent­ly favored mod­el.
• 2. Catal­y­sis (Bond Break­ing and Prod­uct For­ma­tion):
  • The active site, now in close prox­im­i­ty to the sub­strate, facil­i­tates the break­ing of chem­i­cal bonds with­in the sub­strate.
  • This bond break­ing leads to the for­ma­tion of the enzyme-prod­uct com­plex (EP).
  • The chem­i­cal trans­for­ma­tion of the sub­strate occurs at this stage.
• 3. Prod­uct Release and Enzyme Regen­er­a­tion:
  • The enzyme releas­es the new­ly formed product(s) ℗ from its active site.
  • The enzyme returns to its orig­i­nal con­for­ma­tion.
  • The free enzyme is now avail­able to bind with anoth­er sub­strate mol­e­cule and repeat the cat­alyt­ic cycle. This ensures the enzyme can cat­alyze mul­ti­ple reac­tions.