isolating {TAIL ~ the polypeptide} from {HEAD ~ the culture} to obtain a polypeptide 17; and 
isolating { TAIL ~ the polypeptide } from { HEAD ~ the culture } to obtain a polypeptide 17 ; and
OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH