SCANNING TUNNELING MICROSCOPIC AND TRANSMISSION ELECTRON-MICROSCOPIC STUDIES OF CYTOCHROME-C(551) DENATURATION AT THE AIR-WATER-INTERFACE

The morphologies of pseudomonas-cytochrome c551 in directly deposited film, mixed Langmuir-Blodgett (LB) film with an amphiphilic azobenzene derivative, and unfolded LB film have been studied using the scanning tunneling microscopy (STM) and transmission electron microscopy. In t he first two cases, the protein molecule shows a nearly globular struc ture with an external diameter of approximately 5 nm. Occasionally dim er- and trimerlike structures are also observed in such films. In cont rast, the third case gives a rodlike structure whose dimension in leng th falls into a range of 21.5-29.1 nm, indicating the remarkable unfol ding of cytochrome c551 at the air-water interface. Both tertiary and secondary structures of this protein have been virtually lost in such unfolding process. The polypeptide chains of cytochrome c551 molecules in the unfolded LB film are predominantly nearly fully extended, and highly aggregated in a local region, forming a crystalline or a twiste d ropelike structure. Based on the high-resolution STM images of the u nfolded cytochrome c551, a number of intramolecular structures includi ng the locations of heme and several amino acid residues have been dis cussed.