If the quantitatively determinable substance contained in the cells of the reagent is enzyme , this reagent further contains {HEAD ~ a substrate} which specifically interacts with {TAIL ~ the enzyme}  
specifically interacts with
If the quantitatively determinable substance contained in the cells of the reagent is enzyme , this reagent further contains { HEAD ~ a substrate } which specifically interacts with { TAIL ~ the enzyme }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH