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Isopenicillin N isomerase ( epimerase ) has been purified from Streptomyces clavuligerus , and the amino acid sequence of the N - terminus has been determined .
 Isopenicillin N isomerase, epimerase
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: GENE 
Text: {0} 
Answer:
 Isopenicillin N isomerase, epimerase