Biochemistry: Enzymes and Oxidoreductases

General Properties of Oxidoreductases

• Catalyze oxidation–reduction reactions.
• Enzymes are typically proteins that accelerate biochemical reactions.

Types of Enzymes

• Simple Enzyme: Composed solely of protein.
• Conjugated Enzyme: Contains both protein (apoenzyme) and nonprotein (cofactor) components. A holoenzyme is the functional conjugated enzyme.
• Transferase: Transfers functional groups between molecules, with subtypes including transaminases and kinases.
• Hydrolase: Catalyzes hydrolysis reactions, breaking bonds through the addition of water.
• Lyase: Facilitates the addition or removal of groups to/from double bonds without hydrolysis.
• Isomerase: Catalyzes the rearrangement of substrate atoms into isomers.
• Ligase: Joins two molecules with the involvement of ATP.

Models of Enzyme Action

• Enzyme-Substrate Complex: Intermediate formed when a substrate binds to the enzyme's active site.
• Lock-and-Key Model: The active site has a fixed shape, fitting only substrates with complementary geometry.
• Induced-Fit Model: Enzyme's active site adapts to better fit the incoming substrate, allowing for shape changes.

Enzyme Specificity

• Refers to the enzyme's restriction to specific substrates, reactions, or bonds.
• Absolute Specificity: Enzyme catalyzes only one reaction (e.g., catalase for hydrogen peroxide).
• Group Specificity: Acts on substrates with specific functional groups (e.g., carboxypeptidase operates on carboxyl end of peptides).
• Linkage Specificity: Acts on specific chemical bonds (e.g., phosphatases targeting phosphate-ester bonds).
• Stereochemical Specificity: Acts on specific stereoisomers (e.g., L-amino acid oxidase for L-form amino acids).

Factors Affecting Enzyme Activity

• Temperature: Increased temperature raises kinetic energy, affecting reaction rates. Human enzymes peak at 37°C.
• pH: Enzyme activity is influenced by the surrounding pH; optimal pH varies by enzyme (e.g., pepsin at pH 2, trypsin at pH 8).
• Substrate Concentration: Increased substrate concentration enhances activity until saturation, forming a saturation curve.

Enzyme Inhibition

• Enzyme Inhibitor: Slows or halts enzyme function by binding to it.
• Reversible Competitive Inhibition: Inhibitor competes with substrate for active site.
• Reversible Noncompetitive Inhibition: Inhibitor attaches to an alternative site, reducing enzyme activity.
• Covalent Modification: Alters enzyme activity through covalent attachment or removal of chemical groups.

Regulation of Enzyme Activity

• Allosteric Enzymes: Contain multiple protein chains, with regulatory binding sites that influence activity. Positive regulators enhance activity.
• Feedback Control: Regulates the first reaction in a sequence via the product of that pathway.
• Phosphorylation: Addition of phosphate groups acts as an on/off switch for enzyme activity.
• Dephosphorylation: Removal of phosphate groups, affecting enzyme activity inversely.

Protein Kinases

• Enzymes that facilitate the addition of phosphate groups, playing a crucial role in enzyme regulation.

Explore the world of enzymes with a focus on oxidoreductases and their general properties. This quiz will test your knowledge of enzyme structures and classifications, including simple enzymes and transferases. Perfect for biochemistry students looking to reinforce their understanding of enzyme-catalyzed reactions.