Direct observation of uncoated spectrin with atomic force microscope

Spectrin molecules extracted from human blood ceil membrane have been examined by atomic force microscopy (AFM) without using shadowing or staining procedures. A drop of the solution containing spectrin molecules was deposited on the freshly deaved mica substrate. After about 1 min, the residual solution was removed with a piece of filter paper. Afterwards the sample was imaged with a home-made atomic force microscope (AFM) in air in a constant force mode. The obtained AFM images revealed that the spectrin molecules prepared from the above procedures exhibit several kinds of structures as follows: (i) the compact rod-like spectrin heterodimers with a length of around 100 nm; (ii) bent or curved linear tetramers with a length of around 200 nm; (iii) somewhat curved spectrin hexamers, octomers or decamers with lengths of about 300, 400, or 500 nm; and (iv) high oligomers with a length above 1 000 nm.