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: On the other hand , induction of metallothionein ( MT ) by ZnSO ( 4 ) and its role in neuroprotection has been documented .
### Output Text:
On the other hand , induction of <span class="chemical">metallothionein</span> ( <span class="chemical">MT</span> ) by <span class="chemical">ZnSO ( 4 )</span> and its role in neuroprotection has been documented . 