18282
D2 . 63 ( 176 ) A , K373A , D2 . 63 ( 176 ) A - K373A , and the reciprocal mutant with the interacting residues juxtaposed D2 . 63 ( 176 ) K - K373D were characterized using radioligand binding and guanosine 5 ' - 3 - O - ( thio ) triphosphate functional assays .
 guanosine 5 ' - 3 - O - ( thio ) triphosphate
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
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Answer:
 guanosine 5 ' - 3 - O - ( thio ) triphosphate