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: The binding sites from seizure sensitive and resistant mice were equally affected by treatment with dithiothreitol , trypsin or heat .
### Output Text:
The binding sites from seizure sensitive and resistant mice were equally affected by treatment with <span class="chemical">dithiothreitol</span> , trypsin or heat . 