The present invention relates to the use of glutamine synthetase as a proteintherapy (such as enzyme replacement proteintherapy) for the treatment of hyperammonemia. In particular the inventionrelates to the systemic administration of glutamine synthetase.The glutamine synthetase may be provided in conjugated or fusion form, toincrease its half-life in the circulation. Also providedis a pharmaceutical composition comprising glutamine synthetase. The inventionalso relates to the uses, methods and compositionsinvolving a combination of the glutamine synthetase protein and an ammonialowering agent, such as a nitrogen scavenger.
