Multienzyme complexes are groups of enzymes that work together as a single functional unit to catalyze a series of biochemical reactions. These complexes often consist of multiple enzyme subunits, each responsible for catalyzing different steps of a metabolic pathway, forming a highly organized structure that enables efficient and coordinated activity. By being part of a multienzyme complex, enzymes can share substrates more rapidly, protect intermediates from degradation, and minimize side reactions, leading to more efficient metabolic processes.

One classic example of a multienzyme complex is the pyruvate dehydrogenase complex (PDC), which plays a critical role in cellular metabolism, particularly in the conversion of pyruvate into acetyl-CoA. This process is vital for the citric acid cycle (Krebs cycle), a central metabolic pathway that provides energy to the cell. The pyruvate dehydrogenase complex is composed of multiple enzymes, including pyruvate dehydrogenase (E1), dihydrolipoyl transacetylase (E2), and dihydrolipoyl dehydrogenase (E3), along with several coenzymes and cofactors. These subunits work in close proximity, forming a large, multimeric complex that facilitates the transfer of reaction intermediates from one enzyme to the next, ensuring the smooth progression of the reaction sequence.

Another example is the fatty acid synthase (FAS) complex, which is responsible for the biosynthesis of fatty acids.