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: Moreover , the abundance of the alpha ( 1 ) - subunit of the Na - K - ATPase was decreased in the cortex and ISOM , but it remained unchanged in the IM .
### Output Text:
Moreover , the abundance of the alpha ( 1 ) - subunit of the <span class="chemical">Na</span> - <span class="chemical">K</span> - ATPase was decreased in the cortex and ISOM , but it remained unchanged in the IM . 