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: In parallel there was a decrease in ATP synthesis , whereas no difference was observed in subsarcolemmal mitochondria .
### Output Text:
In parallel there was a decrease in <span class="chemical">ATP</span> synthesis , whereas no difference was observed in subsarcolemmal mitochondria . 