What is the primary reason lactate is formed from pyruvate?

The formation of lactate from pyruvate primarily occurs to regenerate NAD from NADH. This process is particularly important during anaerobic conditions, where oxygen availability is limited. In the absence of sufficient oxygen, cells cannot efficiently oxidize NADH in the electron transport chain, leading to a shortage of NAD+. By converting pyruvate into lactate, NADH is oxidized back to NAD+, allowing glycolysis to continue producing ATP, albeit at a reduced efficiency. This is crucial for maintaining energy production, especially in muscle cells during intense exercise when oxygen supply cannot keep pace with energy demand.

The regeneration of NAD+ via lactate formation ensures that glycolysis can proceed, enabling cells to sustain ATP production even in low-oxygen conditions.