13365
Genes involved in apoptosis and DNA damage ( e . g . , SMAC / diablo homolog and DDIT4 / DNA - damage - inducible protein transcript 4 ) had higher mRNA expression levels in eelpout from the harbor compared to the reference site , whereas mRNA expression of genes involved in the innate immune system ( e . g . , complement components and hepcidin ) and protein transport / folding ( e . g . , signal recognition particle and protein disulfide - isomerase ) were expressed at lower levels .
 disulfide
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 disulfide