Pellagra also results from a deficiency of nicotinamide, which is synthesized from tryptophan. Nicotinamide nucleotides are neither oxidized nor reduced during which step of cellular respiration?

Chemiosmosis.

Explanation:

Chemiosmosis may be defined as the movement of ions and molecule down their chemical gradient through the semi-permeable membrane. ATP generation and movement of hydrogen ions during cellular respiration is an example of chemiosmosis.

Pellarga disease is caused due to the deficiency of nicotinamide. Chemiosmosis transport the ions but neither oxidation nor reduction occur in this process of cellular respiration.

Thus, the answer is chemiosmosis.