A 30-year-old female with a history of poor nutrition presents with neurological symptoms, including confusion and muscle weakness. Lab results show elevated levels of pyruvate, suggesting a deficiency in thiamin (vitamin B1). Thiamin is converted to Thiamin Pyrophosphate (TPP), which is essential for pyruvate decarboxylation. Thiamin Pyrophosphate (TPP) functions as which of the following in enzyme catalysis?
