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