For example, {HEAD ~ a disulfide bond} is not reduced at {TAIL ~ the S—S bond} but is displaced to yield an R—S—S fragment ion 
is not reduced at
For example , { HEAD ~ a disulfide bond } is not reduced at { TAIL ~ the S — S bond } but is displaced to yield an R — S — S fragment ion
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH