16722
Finally , we compared the 68 chemicals for their abilities to induce Type I spectral changes of P450 2A13 with the Reverse Type I binding spectra observed with P450 1B1 : 45 chemicals interacted with both P450s 2A13 and 1B1 , indicating that the two enzymes have some similarty of structural features regarding these chemicals .
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Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
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