What molecule acts as the hydrogen donor in lactic acid fermentation?

In lactic acid fermentation, NADH serves as the hydrogen donor. During this anaerobic process, glucose is initially broken down through glycolysis to form pyruvate, generating NADH. When oxygen is not available, cells convert pyruvate into lactic acid, which requires the reduction of pyruvate. In this reaction, NADH donates its electrons and hydrogen ions to pyruvate, thereby regenerating NAD+ in the process. This regeneration of NAD+ is crucial for glycolysis to continue, allowing for the continued production of ATP when oxygen is scarce.

The other options do not play the role of a hydrogen donor in this specific fermentation process. Glucose is the initial substrate that undergoes glycolysis but does not directly donate hydrogen. Pyridoxine is a vitamin (B6) that functions in various metabolic reactions but is not involved in this context. Lastly, oxygen is not present during lactic acid fermentation since this pathway is utilized in anaerobic conditions, making it irrelevant as a hydrogen donor in this situation.