Caption：Proteins from E. coli cells are separated by two-dimensional gelectrophoresis. In the first dimension, (x-axis) the proteins are separated by a pH gradient in which each protein migrates to its isolectric point. The second dimension separates proteins by size on a SDS-polyacrylamide gel. Each spot corresponds to a single polypeptide. There are about 4000 different proteins in E. coli, but some of them are present in very small quantities and cannot be seen on this 2-D gel.
Notes：This figure is from the Swiss-2D PAGE database. You can visit this site and click on any one of the spots to find out more about a particular protein.