SC is {HEAD ~ a conjugated substance} that is said first member of {TAIL ~ a specific binding pair} 
SC is { HEAD ~ a conjugated substance } that is said first member of { TAIL ~ a specific binding pair }
OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL