Describe the important properties of enzymes.

Enzymes are biological catalysts that accelerate reaction rates by lowering activation energy without being consumed

Enzyme specificity arises from a unique active site geometry that binds particular substrates and facilitates specific chemical transformations

Catalytic efficiency is characterized by the turnover number (k cat) and catalytic constant (k cat / Kₘ), reflecting how rapidly and how well an enzyme converts substrate into product

Michaelis–Menten kinetics describe saturation behavior where reaction velocity increases with substrate concentration until reaching Vₘₐₓ when all active sites are occupied

Enzyme activity is highly dependent on temperature

• Activity typically increases with temperature up to an optimum (often 35 °C–40 °C for mammalian enzymes) beyond which heat denatures the enzyme’s tertiary structure

Enzyme activity is highly dependent on pH

• Ionizable amino acid residues at the active site require specific protonation states

• Each enzyme has a narrow pH optimum (e.g., pepsin around pH 2, trypsin around pH 8)

Many enzymes require non-protein cofactors or coenzymes (metal ions, vitamins) for catalytic function

• Metal ions such as Mg²⁺, Zn²⁺, or Fe²⁺ stabilize substrate binding or participate in redox reactions

• Organic coenzymes like NAD⁺, FAD, or coenzyme A shuttle electrons or chemical groups

Enzymes exhibit stereospecificity by distinguishing between stereoisomers of chiral substrates and producing specific stereochemical products

Enzymatic activity can be modulated by inhibitors and activators

• Competitive inhibitors bind the active site and increase apparent Kₘ without affecting Vₘₐₓ

• Noncompetitive inhibitors bind allosteric sites reducing Vₘₐₓ without changing Kₘ

• Allosteric activators or inhibitors bind regulatory sites to shift enzyme between active and inactive conformations

Enzymes can operate under mild physiological conditions of temperature, pH, and pressure, enabling complex metabolic pathways in living systems

Regulatory mechanisms include covalent modification (phosphorylation, acetylation) and zymogen activation, allowing precise temporal and spatial control of enzyme function

Enzymes are recyclable catalysts, returning to their original form after each catalytic cycle and able to process many substrate molecules over time

Enzymes often work in multienzyme complexes or pathways where product of one reaction is substrate for the next, enhancing metabolic efficiency and control