Nanospray spectra of 13 μM GclR protein in 0.1 M NH4HCO3, 1 mM DTT. (A) At 150V declustering voltage, one ion envelope, which is not well resolved. (B) At 250 V declustering voltage, the envelope resolves into the 32–37+ ions of an octamer, accompanied by the appearance of highly charged monomer ions and some evidence of heptamer. There is little evidence of ions from the tetramer or dimer.