3480
In the past four decades of cholinesterase ( ChE ) research , we have seen substantive evolution of the field from one centered around substrate and inhibitor kinetic profiles and compound characterizations to the analysis of ChE structure , first through the gene families and then by X - ray crystallographic determinations of the free enzymes and their complexes and conjugates .
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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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