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: Nonketotic hyperglycinemia is a disorder of amino acid metabolism in which a defect in the glycine cleavage system leads to an accumulation of glycine in the brain and other body compartments .
### Output Text:
Nonketotic hyperglycinemia is a disorder of amino acid metabolism in which a defect in the <span class="chemical">glycine</span> cleavage system leads to an accumulation of <span class="chemical">glycine</span> in the brain and other body compartments . 