Enzyme Classification Flashcards

Enzyme Overview

• Enzymes act as catalysts, significantly increasing the rate of biochemical reactions without being consumed.
• Catalysis refers to the acceleration of a reaction rate by a molecule that remains unchanged after the reaction.

Key Enzyme Characteristics

• Specificity: Enzymes exhibit a preference for certain substrates based on their physical and chemical structure.
• Coenzymes and cofactors are auxiliary substances that may be required for enzymatic activity, with some binding reversibly while others bind tightly.
• Prosthetic groups are tightly-bound coenzymes that do not dissociate from enzymes, though altered during reactions.

Factors Influencing Enzyme Activity

• Substrate and enzyme concentrations affect reaction direction; increased reactants push the reaction right while increased products push it left.
• Temperature can enhance enzyme activity, but excessively high temperatures may denature proteins.
• pH levels influence enzyme activity based on the ionization of catalytic groups; extremes in pH can lead to denaturation.
• Activators and inhibitors can modify enzyme structure and function.

Major Classes of Enzymes

• Oxidoreductases: Catalyze oxidation-reduction reactions, often requiring coenzymes (e.g., dehydrogenases, oxidases).
• Transferases: Facilitate group transfers (e.g., kinases, transaminases).
• Hydrolases: Catalyze bond cleavage with water addition (e.g., peptidases, amylases).
• Lyases: Induce bond cleavage without water (e.g., decarboxylases, synthases).
• Isomerases: Assist in rearranging isomers (e.g., mutases, racemases).
• Ligases: Form bonds using energy from high-energy compounds like ATP (e.g., synthetases, carboxylases).

Coenzymes and Their Associated Enzymes

• For Oxidoreductases:
  • Cu2+/Cu+ in Cytochrome C oxidase
  • FAD/FADH2 in Succinate Dehydrogenase
  • NAD+/NADH in Lactate Dehydrogenase and Alcohol Dehydrogenase
• For Transferases:
  • ATP/ADP in various kinases
  • Pyridoxal phosphate in aminotransferases
• For Ligases:
  • ATP and Biotin in Pyruvate Carboxylase

Enzyme Localization and Significance

• Enzymes are precisely located in organs, tissues, and cells based on their specific functions; for example, hydrolases are found in lysosomes, while DNA polymerase is localized in nuclei.
• Tissue-specific enzymes reflect the different metabolic needs of organs (e.g., liver vs. adipose tissue).

Proenzymes and Isozymes

• Proenzymes (zymogens) contain activation sites which, upon cleavage, produce active enzymes with variations in amino acid sequences.
• Isozymes are enzymes with different amino acid sequences but catalyze the same reaction, reflecting genetic differences in polypeptides (e.g., multiple forms of lactate dehydrogenase).

Clinical Relevance of Isozyme Analysis

• Elevated levels of lactate dehydrogenase (LDH) in plasma can indicate tissue damage, making isozyme analysis a valuable tool in diagnosing conditions like myocardial infarction.
• Changes in LDH isozymes can reflect specific health issues (e.g., increased levels post-acute myocardial infarction or acute hepatitis).