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: RATIONALE : gamma - Vinyl GABA ( GVG ) irreversibly inhibits GABA - transaminase .
### Output Text:
RATIONALE : <span class="chemical">gamma - Vinyl GABA</span> ( <span class="chemical">GVG</span> ) irreversibly inhibits <span class="chemical">GABA</span> - transaminase . 