The column may be closed at {HEAD ~ the ends} and shaken and washed with {TAIL ~ an enzymatic buffer} 
The column may be closed at { HEAD ~ the ends } and shaken and washed with { TAIL ~ an enzymatic buffer }
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL