The in vitro renaturation and assembly of cytokeratin molecules to form intermediate filaments (IF) illustrates that these molecules contain all of the structural information necessary for IF information. These molecules contain nine structural domains: the aminoand carboxyterminal extra helical regions, and three conserved extra helical segments that separate four helical rod-like domains. Chymotrypsin treatment of these molecules removes the end-peptide domains and inhibits the self-assembly process.We have examined the renaturation and assembly of cytokeratin molecules using solution conditions that favor the presence of intermediate forms of IF organization. Dialysis against low salt buffers revealed the presence of bead-like chains of filaments in which the 6-8-nm beads are separated by a distance of 21 nm. These data suggest that a lateral stagger of protofilaments was among the primary events in IF assembly. Chymotrypsin-modified cytokeratin enriched for a-helix barely initiated a turbidity increase at conditions favoring selfassembly. Addition of small amounts of intact cytokeratin accelerated the rate and extent of this reaction. These results indicate that the nonhelical peptides on intact cytokeratin potentiate the assembly of IF by orientating the stagger of laterally associated protofilaments.

An immunohistochemical technique was used on paraffin‐embedded tissues of four cases of calcifying epithelial odontogenic tumors (CEOT). These studies were performed to gain an additional understanding of the nature of amyloid‐like deposits in these tumors. For these studies antibodies to Type IV collagen, laminin. and the five classes of intermediate filament proteins were employed. In all of the tumors examined basement membrane components and intermediate filament proteins (cytokeratin) were demonstrated both in the epithelial tumor islands and within the extracellular amyloid‐like deposits. Antibodies to vimentin intermediate filaments were localized only in the stromal fibroblasts. Limited proteolysis or the use of a chaotropic agent was required to express the antigenic determinants present. These studies substantiate the presence of basement membrane components in the amyloid‐like deposits of CEOT. In addition, these extracellular deposits are shown to be heterogenous in composition by the immunohistochemical demonstration of cytokeratin intermediate filament proteins.

Prolonged storage of PCs was associated with decreased PLT-adhesive capacities and enhanced PCA. Current preparation procedures and storage media have important limitations for preserving PCs for longer than 1 week. PLTs in PCs retain residual amounts of TF as assessed by immunocytochemical and functional assays. The origin and hemostatic significance of this TF should be investigated further.