5940
Comparison with the crystal structure of Desulfovibrio gigas , Dg , Fd ( Kissinger et al . , 1991 ) reveals a very similar folding topology , although several secondary structural elements are extended in Pf relative to Dg Fd .
 Fd, Fd
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: GENE 
Text: {0} 
Answer:
 Fd, Fd