What are Enzymes?

Scientific concepts, discoveries, and nature phenomena

Role and discovery of enzymes

• Enzymes control and accelerate chemical reactions in the human body and other biochemical processes.
• Historical discovery (1833): French chemist Anselme Payen is credited with first identifying and naming the “vital force” behind these reactions as “enzyme.”
• Enzyme definition: Substances—typically proteins and sometimes RNA—that speed up biochemical reactions by acting on specific substrates.
• Specificity: Enzymes are highly selective about which substrates they bind to and modify.

Mechanism of enzyme action (catalysis)

• Enzymes lower reaction activation energy, making reactions start more easily.
• They bind substrates and facilitate bond-breaking and bond-forming by positioning substrates in favorable orientations.

Active site

• A specific region of the enzyme where the substrate binds and catalysis occurs.
• Its size, shape, and chemical properties are determined by an arrangement of amino acids, making it uniquely suited for a particular substrate.

Cofactors

Non-protein components required for many enzymes to function.

• Cations (metal ions): Temporarily bind to activate the enzyme.
• Organic molecules: Such as vitamins / coenzymes that join temporarily.
• Prosthetic groups: Permanently bound cofactor components.

Holoenzyme vs. apoenzyme

• Holoenzyme = apoenzyme + coenzyme
• Apoenzyme: the inactive protein portion
• Coenzyme / cofactor: the non-protein component needed for activity

Models of enzyme action

• Lock and Key hypothesis:
  • Substrate fits the enzyme’s active site without changing the enzyme’s shape.
  • Specific fit is analogous to a key fitting a lock.
• Induced Fit hypothesis:
  • Upon substrate binding, the enzyme changes shape to bind more tightly and achieve optimal catalysis.

Environmental effects on enzyme function

Enzyme active sites are sensitive to conditions that alter bonding/shape:

• Temperature
  • “Suitable temperature” is stated as 37°C for enzyme function in the context of the human body.
  • Deviations above/below reduce binding or can denature enzymes.
• pH
  • Changes in pH can affect the acidic/basic amino acid residues in the active site.
  • Extreme pH can denature enzymes.
• Enzyme concentration
  • Increasing enzyme concentration increases reaction rate up to a point.
  • Beyond a certain concentration, additional enzyme may not increase rate (implied saturation).
• Substrate concentration
  • Increasing substrate concentration increases reaction rate by increasing substrate–enzyme collisions.
  • Effect holds only up to a certain concentration (implied saturation).

Inhibition of enzyme activity

• Inhibitors reduce or stop enzyme activity by interfering with function—typically by blocking or distorting the active site or other parts of the enzyme.
  • Competitive inhibitors:
    • Bind/occupy the active site, preventing substrate binding.
  • Non-competitive inhibitors:
    • Bind to sites other than the active site and distort the enzyme’s shape, reducing catalytic activity.

Researchers / sources featured

• Anselme Payen (French chemist; associated with discovery/naming of “enzyme” in 1833)