I am considering nitrogen fixation and in my lecture notes, there is the statement 

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> The glutamine synthetase- glutamate synthase system requires use of an ATP molecule as well as reducing power. Although it is energy intensive compared with glutamine synthase, the Km of glutamine synthetase is much lower than that of glutamate dehydrogenase. When NH3 is scarce, the additional ATP investment is worthwhile. 
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Try as I might, I can't find anything about glutamine synthase. Searches online seem to only return results for glutamine synthetase. I was wondering if this is a mistake in my notes? If so, I can only think that this should be 'glutamate dehydrogenase', in which case the statement is about comparing the method used by animals and fungi (which use glutamate dehydrogenase to fix nitrogen via a Schiff base) compared with plants and other microorganisms (which use the glutamine synthetase glutamate synthase method).

This is my first exposure to learning about nitrogen fixation, so I would very much are coated any clarification.

Also, I was wondering what the general difference is between a 'synthase' enzyme and 'synthetase', if there is one.