SynopsisThe adsorption of globular proteins a t solidhiquid or liquidhiquid interfaces provides evidence of unfolded molecular conformation. Proteins with high apolar character are strongly unfolded, while those with high polar character are generally incompletely unfolded. Structural changes of globular proteins a t adsorption on mercury electrodes were studied by ac polarography and capacity-time curves. The surface area per molecule of nine globular proteins was determined from the adsorption kinetics a t the dropping mercury electrode. For all the proteins investigated, this value was greater than the maximal molecular cross section of the native proteins. The surface area was about 19 Az per amino acid residue, which coincides with the value for unfolded proteins a t the water/air interface. Differences between dropping mercury electrode and hanging drop mercury electrode occurred only with lysozyme and phosphorylase; for the other proteins, the structure of the adsorption layer was independent of the time of interaction at the electrode. Since not all of the reducible groups of the adsorbed proteins come into contact with the electrode, the flattening should be incomplete.