DIRECT OBSERVATION OF ENZYME-ACTIVITY WITH THE ATOMIC-FORCE MICROSCOPE

The height fluctuations on top of the protein lysozyme adsorbed on mic a were measured locally with an atomic force microscope operated in ta pping mode in liquid. Height fluctuations of an apparent size of 1 nan ometer that lasted for about 50 milliseconds were observed over lysozy me molecules when a substrate (oligoglycoside) was present. In the pre sence of the inhibitor chitobiose, these height fluctuations decreased to the level without the oligoglycoside. The most straightforward int erpretation of these results is that the height fluctuations correspon d to the conformational changes of lysozyme during hydrolysis. It is a lso possible, however, that the height fluctuations are, at least in p art, the result of a different height or elasticity of the transient c omplex of lysozyme plus the substrate.