B. subtilis GlcK can form a homodimer molecule. (A) GlcK dimerization is shown on 12% SDS-PAGE under reducing condition (1) and non-reducing condition (2). Molecular mass standard 70L (Sigma, Deisenhofen, Germany) with indicated size was used. (B) Cross-link experiment of GlcK was separated on an 8% polyacrylamide gel under non-reducing condition. Non-cross linked GlcK (1) demonstrates both monomeric and homodimeric form of GlcK (*), oxidized GlcK with 1% H2O2 (2), and 10 mM CuSO4.2H2O and 30 mM 1,10-phenantroline (3) shows only the homodimer. A MALDI-TOF mass spectrum shows the homodimer (70.4 kDa) and monomer (35.2 kDa) of GlcK. The 17.6 kDa peak is the protonated form of the sample.