Substructures of neurofilaments.

The results of this investigation indicate that neurofilaments of mammals (human and rabbit) are composed of four protofilaments each of which is formed of globular units connected by longitudinal bars. A cross-view of neurofilaments reveals the presence of four globular units, 20-25 A in diameter, connected by four transverse bars, 25-30 A in length. Two of the transverse bars appear more electron-dense (darker) than the remaining two. A longitudinal view of neurofilaments shows two protofilaments bonded by the darker of the transverse bars to form a two-stranded band. The remaining two protofilaments form a band in a similar manner. The two two-stranded bands, wrapped helically, form a four-stranded neurofilament. The axial periodicity between twists along each neurofilament ranges from 200 A to 270 A. A three-dimensional diagram of neurofilament structure is presented.