In molecular biology, a multienzyme complex is a protein complex containing several copies of one or more enzymes packed into one macromolecular assembly. Multienzyme complexes carry out a single or multi-step biochemical reaction taking place within cells. It allows the cell to segregate certain biochemical pathways into one place in the cell.^[1]

Examples include pyruvate dehydrogenase, fatty acid synthetase, glutamine synthetase, proteasome, rubisco.

A multienzyme complex that functions in the histidine biosynthesis pathway has been studied at the biochemical and genetic level in the fungus Neurospora crassa. A gene (His-3) was found to encode a protein that functions as a multienzyme complex having three distinct enzymatic activities in the biosynthesis pathway.^[2] A genetic analysis of mutants defective in the N. crassa histidine pathway indicated that the individual activities of the multienzyme complex occur in discrete regions of the His-3 genetic map. This finding suggested that each of the activities of the multienzyme complex are encoded separately from each other, but within the same gene.^[2] Some His-3 mutants were also found that lacked all three activities simultaneously, suggesting that some mutations can cause loss of function of the whole multienzyme complex.

• Quaternary structure
• Protein complex
• Macromolecular assembly
• Biomolecular complex