Enzymes are nature's molecular machines, driving countless biochemical reactions in our bodies. These protein catalysts are marvels of structure and function, with their intricate folds and specific active sites tailored for precise tasks.

Enzyme activity is a delicate dance influenced by temperature, pH, and substrate availability. Understanding these factors is crucial for harnessing enzymes in medicine and industry, from designing targeted drugs to creating efficient biofuel production processes.

Enzyme Structure and Composition

Structure and composition of enzymes

• Enzymes act as biological catalysts composed of amino acids linked through peptide bonds
• Primary structure forms linear sequence of amino acids determining protein identity
• Secondary structure creates local folding patterns (alpha helices and beta sheets) via hydrogen bonding
• Tertiary structure develops overall 3D shape through various interactions between amino acid side chains
• Quaternary structure involves multiple protein subunits assembling into functional complex (hemoglobin)
• Protein folding shapes enzyme function through:
  • Hydrophobic interactions clustering non-polar residues in protein core
  • Hydrogen bonding stabilizing secondary structures and maintaining tertiary fold
  • Disulfide bridges covalently linking cysteine residues for added stability (insulin)
  • Salt bridges forming electrostatic attractions between charged amino acids
• Cofactors and coenzymes enhance enzymatic activity:
  • Metal ions serve as electron donors/acceptors or structural stabilizers (zinc in carbonic anhydrase)
  • Organic molecules act as temporary carriers of specific chemical groups (NAD+ in dehydrogenases)

Role of enzyme active sites

• Active site forms specific region where substrate binding occurs
• Typically located in pocket or cleft of enzyme structure to maximize contact with substrate
• Lock and key model proposes rigid active site fits specific substrate like key in lock
• Induced fit model suggests active site changes shape to accommodate substrate upon binding
• Substrate binding involves weak, non-covalent interactions (hydrogen bonds, van der Waals forces)
• Transition state stabilization lowers activation energy of reaction by:
  1. Orienting substrates in favorable positions
  2. Providing catalytic groups to facilitate bond breaking/forming
  3. Excluding water to create favorable reaction environment

Enzyme Specificity and Activity

Enzyme specificity in biology

• Substrate specificity enables enzymes to catalyze reactions with particular substrates (lactase with lactose)
• Stereochemical specificity allows enzymes to distinguish between stereoisomers (L-amino acid oxidase)
• Reaction specificity ensures enzymes catalyze specific types of chemical reactions (hydrolases, transferases)
• Specificity regulates metabolism by:
  • Controlling biochemical pathways through selective catalysis
  • Preventing unwanted side reactions that could produce harmful byproducts
• Applications in medicine and biotechnology include:
  • Designing drugs to target specific enzymes (statins inhibiting HMG-CoA reductase)
  • Engineering enzymes for industrial processes (detergent enzymes, biofuel production)

Factors affecting enzyme activity

• Temperature influences enzyme activity:
  • Increased temperature raises reaction rate up to optimum by increasing molecular motion
  • Denaturation occurs at high temperatures disrupting protein structure
• pH affects enzyme activity:
  • Each enzyme has optimal pH range for maximal activity (pepsin in stomach acid)
  • pH alters ionization state of amino acid side chains affecting substrate binding and catalysis
• Substrate concentration impacts reaction rate:
  • Follows Michaelis-Menten kinetics describing relationship between substrate concentration and reaction velocity
  • Equation: $v = \frac{V_{max}[S]}{K_m + [S]}$ where v = reaction velocity, $V_{max}$ = maximum velocity, [S] = substrate concentration, $K_m$ = Michaelis constant
• Enzyme concentration directly proportional to reaction rate at low concentrations
• Inhibitors modulate enzyme activity:
  • Competitive inhibitors bind active site (penicillin blocking bacterial cell wall synthesis)
  • Non-competitive inhibitors bind allosteric site altering enzyme shape
  • Uncompetitive inhibitors bind enzyme-substrate complex
• Allosteric regulation occurs when effector molecules bind to sites distinct from active site
• Covalent modification alters enzyme activity through addition or removal of chemical groups (phosphorylation in glycogen metabolism)