The pentose phosphate pathway serves as the primary source of NADPH in erythrocytes to maintain reduced glutathione and protect against oxidative stress, representing a foundational biochemical fact that requires no citation.
The claim is a textbook biochemical fact regarding erythrocyte metabolism (the pentose phosphate pathway supplying NADPH for antioxidant defense via glutathione). Per instructions, trivially true biological facts and everyday observations are classified as common knowledge, requiring no citation or paper assignment.