 Studies generally employ D-alanine, D-aspartate, and D-glutamate, as they represent the most common D-amino acids  in living organisms.
<clarity>  Studies generally employ D-alanine, D-aspartate, and D-glutamate, as they represent the most common D-amino acids  in living organisms.
 Studies generally employ D-alanine, D-aspartate, and D-glutamate, as they signify the most common D-amino acids in living organisms.