Review Question - QID 210466

A 42-year-old woman presents to her primary care physician for fatigue and blurry vision. She is a refugee from Syria who arrived in the United States 1 week ago. She has lived for the last 8 months in a refugee camp. She worked at a grocery store in Syria before being displaced from her home. She has one son who is 9 years old and was seen by a pediatrician the day prior. She reports that while she was in the refugee camp, she ate very little and gave most of her food to her son to ensure that he stayed healthy. She denies any past medical history and takes no medications. She does not smoke or drink alcohol. Her temperature is 97.8°F (36.6°C), blood pressure is 108/68 mmHg, pulse is 102/min, and respirations are 18/min. On exam, she appears fatigued but is fully cooperative with the examination. There are fissures at the corners of her mouth. A slit lamp examination reveals corneal vascularization in both eyes. Her tongue is darkly erythematous. This patient is most likely deficient in a vitamin that has which of the following functions?