Protein samples were mixed 1:1 in SDS sample buffer (4% SDS, 17.4% glycerol, 0.003% bromophenol blue, 0.125 M Tris, 8 mM IAA (iodoacetamide)) with or without reducing agent (2-mercaptoethanol) as indicated, boiled for 3 min, spun at 20,000×g for 1 min, and loaded onto a 12% or 15% running gel with a 5% stacking gel. Gels were run at 180 V, 40 mA for 50 min.