In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: Amino acids 5 and 7 , two potent and selective competitive GluR5 KA receptor antagonists , exhibited high GluR5 receptor affinity over other glutamate receptors .
### Output Text:
Amino acids 5 and 7 , two potent and selective competitive GluR5 <span class="chemical">KA</span> receptor antagonists , exhibited high GluR5 receptor affinity over other <span class="chemical">glutamate</span> receptors . 