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: Activation of the nuclear enzyme poly ( ADP - ribose ) polymerase ( PARP ) by oxidant - mediated DNA damage is an important pathway of cell dysfunction and tissue injury in conditions associated with oxidative stress .
### Output Text:
Activation of the nuclear enzyme <span class="chemical">poly ( ADP - ribose )</span> polymerase ( PARP ) by oxidant - mediated DNA damage is an important pathway of cell dysfunction and tissue injury in conditions associated with oxidative stress . 