Enzymes and Cofactors

Cofactors and Coenzymes

• TPP (Thiamine Pyrophosphate) is synthesized from Vitamin Thiamine
• FAD (Flavin Adenine Dinucleotide) and FMN (Flavin Mononucleotide) are synthesized from Vitamin Riboflavin
• Examples of coenzymes include FAD, FMN, TPP, and others

Types of Enzymes

Oxidoreductases

• Enzymes involved in oxidation-reduction reactions
• Example: Superoxide Dismutase (SOD), mutations of which lead to Amyotrophic Lateral Sclerosis

Hydrolases

• Enzymes that cleave molecules using water
• Example: Tissue Plasminogen Activator, which cleaves Plasminogen to Plasmin to dissolve clots

Ligases

• Enzymes that catalyze synthetic reactions, forming covalent bonds at the expense of high-energy phosphate bonds (usually ATP)
• Example: Pyruvate Carboxylase

Enzyme Activity

• The Induced Fit model is the most accepted model, stating that binding of substrate to enzyme induces a conformational change in the enzyme, directing appropriate amino acids to the active site
• Factors affecting enzyme activity: availability of enzyme, optimum pH, optimum temperature, coenzymes, and cofactors

Optimum pH and Temperature

• Enzymes work best at optimum pH and temperature
• Examples: Salivary Amylase catalyzes best at pH 7, Pepsin catalyzes best at pH 2, and high temperatures can cause denaturation of enzymes

Km and Vmax

• Km is the substrate concentration at which ½ Vmax is reached
• Low Km value indicates strong affinity of enzyme towards substrate, while high Km reflects weak affinity
• Vmax is the maximum rate of enzyme activity, where all enzymes are saturated with substrate and are in the ES (Enzyme-Substrate) complex

Hexokinase and Glucokinase

• Both catalyze phosphorylation of glucose
• Hexokinase: present in all cells except hepatocytes and β-cells of pancreas, has low Km (high affinity) for glucose, and works even at low glucose concentrations
• Glucokinase: present in hepatocytes and β-cells of pancreas, has high Km (low affinity) for glucose, and removes glucose from circulation only after a meal

Acetaldehyde Dehydrogenase

• Required to detoxify acetaldehyde from breakdown of alcohol
• Two types: low Km form and high Km form, with the low Km form breaking down acetaldehyde more efficiently

Competitive Inhibition

• A type of reversible inhibition where the inhibitor is a structural analog of the substrate and binds to the active site of the enzyme
• Examples: Sulfonamides, Trimethoprim, Dicoumarol, Captopril, and Allopurinol

Test your knowledge of enzymes, cofactors, and coenzymes, including their functions, synthesis, and examples. Learn about oxidoreductases, hydrolases, lyases, and ligases, and how they relate to various biological processes.