First, the labeling agent must contain {HEAD ~ a label}; second, the labeling agent must physically or chemically bind to the binding partner or {TAIL ~ the binding agent} 
First , the labeling agent must contain { HEAD ~ a label } ; second , the labeling agent must physically or chemically bind to the binding partner or { TAIL ~ the binding agent }
OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL