Vitamin coenzymes — the vitamin niacin (vitamin B3) is a constituent of which canonical redox coenzyme?

Introduction / Context:
Niacin (as nicotinamide) forms the vitamin-derived core of the widely used redox cofactors NAD+ and NADP+. Recognizing this linkage is fundamental in metabolism and nutrition.

Given Data / Assumptions:

• NAD+ = nicotinamide adenine dinucleotide.
• Nicotinamide ring accepts hydride (H−) to form NADH.
• Pyridoxal phosphate is derived from vitamin B6, not niacin.
• Ferredoxin is an iron–sulfur protein, not a nucleotide coenzyme.

Concept / Approach:
Map vitamin to coenzyme: niacin → nicotinamide moiety in NAD+/NADP+.

Step-by-Step Solution:
Identify niacin’s biochemical role as nicotinamide.Recall composition of NAD+: adenine nucleotide + nicotinamide nucleotide.Eliminate B6-derived PLP and protein ferredoxin.Select “NAD+.”

Verification / Alternative check:
Biochemistry references consistently attribute dehydrogenase reactions to NAD+/NADP+ using the nicotinamide ring.

Why Other Options Are Wrong:
PLP derives from B6; ferredoxin is unrelated; “pyrophosphate” is not a coenzyme name; FAD derives from riboflavin (B2).

Common Pitfalls:
Confusing niacin (B3) with riboflavin (B2) due to both participating in redox chemistry.

Final Answer:
NAD+.