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: This non - receptor mediated inhibition requires de novo synthesis for restoration of functional GABA catabolism .
### Output Text:
This non - receptor mediated inhibition requires de novo synthesis for restoration of functional <span class="chemical">GABA</span> catabolism . 