Glucose labeled with ¹⁴ C at C-6 is added to a solution containing the enzymes and cofactors of the oxidative phase of t
The principle of enzyme catalysis and lipid structure explains that substrate affinity, transition state stabilization and phospholipid composition govern function. Hence C5 of ribulose 5-phosphate fits best because it reflects catalytic efficiency and membrane organization, as documented in authoritative sources on biochemistry.
Ref: Lehninger Principles of Biochemistry, Chapter 9, Lipids and Membranes, explains phospholipid components, glycerol, fatty acids, phosphate group and membrane structure providing foundation for lipid biochemistry.