4FB-modified proteins are stable at 4oC for up to one year. HyNic-modified proteins are not stable and should be used the same day they are modified, preferably. HyNic-modified proteins can be stored at –80?C in small, single-use aliquots, in conjugation buffer. No need to add glycerol. And, do not re-freeze after used – reason for the aliquots. Should be good for several months. You want the proteins frozen, not moving around in solution, with possible HyNic-amino group interaction.