The enzymes in Pseudomonas aeruginosa that help the bacteria use ammonia were studied. Glutamine synthetase is controlled by how much nitrogen is available, being active when nitrogen is low and inactive when there is excess nitrogen. Two types of glutamate dehydrogenase were found, with different sizes and responses to nitrogen and glutamate levels. One type is repressed when nitrogen is limited or when growing on glutamate, while the other is activated by glutamate. Glutamate synthase is turned off by glutamate but not by too much nitrogen.