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Oocyte of Xenopus laevis is one of the most frequently used heterologous expression systems , which are used to design and analyze specific combinations of GABA A receptor subunits .
 Chemical: GABA
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: GABA