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 mRNA levels of LDLr and ERK1 / 2 as well as protein levels of total and activated forms of ERK1 / 2 in rat liver were evaluated by Western blotting and quantitative real time polymerase chain reaction analysis .
### Output Text:
Moreover mRNA levels of LDLr and ERK1 / 2 as well as protein levels of total and activated forms of ERK1 / 2 in rat liver were evaluated by Western blotting and quantitative real time polymerase chain reaction analysis . 