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