Single enzyme molecules
(a) A layer of fatty-acid molecules, one of the major constituents of cell membranes, is adsorbed on a mica substrate. The holes have a depth of 5 nm, corresponding to twice the length of the fatty-acid molecules. The image is formed by scanning the tip of the atomic force microscope across the sample. (b) When the enzyme phospholipase A2 is added, it digests canals through the membrane, suggesting that we are observing the activity of a single enzyme molecule.