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: Both catalytic parameters Km = 265 uM for BTC , two times higher than that of the atypical enzyme , and a low Vmax are consistent with the absence of activity against suxamethonium .
### Output Text:
Both catalytic parameters Km = 265 uM for <span class="chemical">BTC</span> , two times higher than that of the atypical enzyme , and a low Vmax are consistent with the absence of activity against <span class="chemical">suxamethonium</span> . 