ATP + L-glutamate + NH4(+) = ADP + H(+) + L-glutamine + phosphate Homooctamer. In pea there are distinct isozymes in leaves, roots and nodules. Irreversibly inhibited by the herbicide L-phosphinothricin (PPT). This root isozyme is responsible for the assimilation of ammonia fixed by bacteroids. Belongs to the glutamine synthetase family.