Atomic Force Microscopy Investigation of Ribonuclease A

Ribonuclease A (RNase A) molecules have been adsorbed onto mica surfaces from aqueous solution at pH 7.4. Atomic force microscopy (AFM) images of native RNase A show aggregates of monomers each having a diameter of 9 nm. This is consistent with a globular unit the size of which would be substantially larger than that expected for a 13-kDa protein. These experiment suggest that the RNase A oligomer subunits exist as a multimeric complex with the 13-kDa protein.