19568
Cloning of a short - period circadian mutant , Past - time , revealed a glycine to glutamate missense mutation in Fbxl21 , an F - box protein gene that is a paralog of Fbxl3 that targets the CRY proteins for degradation .
 glycine, glutamate
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 glycine, glutamate