Question 64:
Enzymes that are involved in the transfer of electrons (hydride ions or H atoms) are called:
The correct answer is (C) Oxidoreductases.
Enzymes that transfer electrons (hydride ions H⁻ or hydrogen atoms) in redox reactions are oxidoreductases (EC 1 class), catalyzing oxidation of one substrate (electron donor) and reduction of another (electron acceptor), often using NAD⁺/NADP⁺ cofactors.
Option Breakdown
(A) Transferases
Transferases (EC 2) move functional groups like methyl, glycosyl, or phosphate between molecules (e.g., kinases, transaminases), not electrons.
(B) Hydrolases
Hydrolases (EC 3) catalyze hydrolysis reactions breaking bonds via water addition (e.g., proteases, lipases), without electron transfer.
(C) Oxidoreductases
Correct; includes dehydrogenases (H⁻/H- transfer), oxidases (O₂ reduction), reductases. Examples: lactate dehydrogenase (NADH ↔ NAD⁺), cytochrome c oxidase.
(D) Ligases
Ligases (EC 6) join two molecules with ATP hydrolysis (e.g., DNA ligase, glutamine synthetase), forming bonds without redox activity.
Introduction to Enzymes Transfer Electrons Hydride
Enzymes transfer electrons hydride ions or H atoms belong to oxidoreductase class (EC 1), fundamental in respiration, photosynthesis, and metabolism. GATE Life Sciences tests IUB enzyme classification mastery.
Oxidoreductase Mechanism
General reaction: AH₂ + B → A + BH₂, where hydride (H⁻ from NADH) or H- transfers via flavins/FAD, hemes, or metal centers. Dehydrogenases use pyridine nucleotides; oxidases employ O₂.
Membrane-bound form ETC complexes I-IV.
Enzyme Classes Comparison Table
| Class | EC # | Function | Electron Transfer? |
|---|---|---|---|
| Transferases | 2 | Group transfer | No |
| Hydrolases | 3 | Hydrolysis | No |
| Oxidoreductases | 1 | Redox (e⁻/H⁻ transfer) | Yes |
| Ligases | 6 | Bond formation (ATP) | No |
Identifies enzymes transfer electrons hydride precisely.
Exam Context for Life Sciences
Builds on prior Kd (binding affinity affects kcat/Km redox ratios), macrophages (NADPH oxidase ROS), lipids (quinone carriers); memorize EC 1=oxidoreductase first in IUB list for PYQs.
