In the linked reaction scheme, why are only L-glutamate and N-acetyl glutamate considered, and not acetyl-CoA or the coenzyme? Is this because L-glutamate and N-acetyl L-glutamate are the main compounds to be considered? Why are they the main compounds being considered? Are these two compounds (L-glutamate and N-acetyle L-glutamate) the ligands?
The synthesis of N-acetylglutamate is mediated by the enzyme N-acetylglutamate synthase. This enzyme has L-glutamate as its substrate and uses acetyl-coenzyme A as a co-enzyme acetyl donor. Acetylcoenzyme A (Acetyl-CoA) is generally abbreviated in structural formulas, because it is a relatively complex molecule. The only thing of relevance is the acetyl group which is transferred from a thiol group to L-glutamate.
Note that ligands is a term reserved for molecules binding to receptors; substrates is the proper term for intermediates in enzymatic reactions.
N-acetylglutamate synthesis. Source: The Medical Biochemistry page