8236
These residues , Ile244 at the extracellular end of transmembrane helix 3 , and Tyr318 at the COOH - terminal portion of extracellular loop 2 , are replaced by Leu and Ile in the PTH - 1 receptor , respectively .
 PTH - 1 receptor
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: GENE 
Text: {0} 
Answer:
 PTH - 1 receptor