The smallest entity we observed was the dimer. Our measurements therefore ruled out isolated monomer exchange by way of subunit diffusion in solution. On the other hand, what we did observe was significant numbers of whole SOD molecules lying side by side. It became obvious that exchange was taking place by some “docking mechanism”. The Whiteshell Lab then carried out HPLC (High Performance Liquid Chromatography) on irradiated solutions that showed that nothing smaller than whole SOD molecules were present.