Q.32 Match the entries inGroup I with the enzymes inGroup II.
Group I Group II
P. NAD+ 1. Glutathione peroxidase
Q. Selenium 2. Nitrogenase
R. Pyridoxal phosphate 3. Lactate dehydrogenase
S. Molybdenum 4. Glycogen phosphorylase
(A) P-3, Q-2, R-4, S-1 (B) P-4, Q-1, R-3, S-2
(C) P-3, Q-1, R-4, S-2 (D) P-3, Q-4, R-2, S-1
Enzyme Cofactor Matching: NAD+, Selenium, PLP, Molybdenum
Correct Answer: (C) P-3, Q-1, R-4, S-2. NAD+ serves lactate dehydrogenase, selenium enables glutathione peroxidase, pyridoxal phosphate activates glycogen phosphorylase, and molybdenum powers nitrogenase.
Cofactor-Enzyme Roles
Metalloenzymes and vitamin-derived cofactors catalyze essential reactions in metabolism and redox homeostasis. Trace elements like selenium integrate as selenocysteine, while organic cofactors like NAD+ transfer hydride equivalents in dehydrogenases.
Correct Matching Breakdown
P. NAD+ → 3. Lactate dehydrogenase. NAD+ accepts hydride from lactate, forming NADH in anaerobic glycolysis; LDH catalyzes L-lactate + NAD+ ⇌ pyruvate + NADH + H+.
Q. Selenium → 1. Glutathione peroxidase. Selenocysteine (Sec) at the active site reduces H₂O₂ and lipid hydroperoxides: 2GSH + H₂O₂ → GSSG + 2H₂O, preventing oxidative damage.
R. Pyridoxal phosphate → 4. Glycogen phosphorylase. PLP forms a Schiff base with lysine, orienting glycogen for phosphorolytic cleavage: (glycogen)n + Pi → (glycogen){n-1} + glucose-1-P.
S. Molybdenum → 2. Nitrogenase. MoFe-protein contains molybdenum in the FeMoco cluster, catalyzing N₂ + 8H+ + 8e- + 16ATP → 2NH₃ + H₂ + 16ADP + 16Pi.
Option Analysis
Option (A) P-3, Q-2, R-4, S-1 incorrectly pairs selenium with nitrogenase (Mo-specific) and molybdenum with GPx (selenoprotein).
Option (B) P-4, Q-1, R-3, S-2 mismatches NAD+ to glycogen phosphorylase (PLP-dependent) and PLP to LDH (NAD+ hydride transfer).
Option (D) P-3, Q-4, R-2, S-1 wrongly assigns selenium to phosphorylase (PLP cofactor) and molybdenum to GPx (selenium-requiring).
Biochemical Relevance
These pairings highlight micronutrient deficiencies’ metabolic impacts—selenium depletion cripples antioxidant defense, molybdenum limits nitrogen fixation, PLP shortages impair glycogenolysis, and NAD+ deficits disrupt fermentation.
