Immunoreactivity to the pre-core box antibody shows that most glycine-rich beta-proteins accumulate in lepidosaurian beta-layer and in the corneous layer of crocodilian and turtle epidermis.

The differentiation of the corneous layers of reptilian epidermis has been analyzed by ultrastructural immunocytochemistry using specific antibodies against the conserved pre-core box region of their keratin-associated beta-proteins (KAbetaPs, formerly indicated as beta-keratins) and silver-intensification. The epitope analysis in the sequences of different reptilian KAbetaPs indicates that this antibody recognizes mainly glycine-rich beta-proteins in lizards and snakes. The immunoreactivity of the beta-layer of the tuatara to this antibody also suggests that a similar epitope is present in beta-proteins of this relict species. In crocodilians the antibody recognizes glycine-rich beta-proteins, so far representing all the known crocodilian KAbetaPs. In hard-shelled turtle the antibody labels mainly type 1 KAbetaPs that represent most types found in this turtle. The antibody does not label the corneous layer of the soft-shelled turtle that contains exclusively type 2 KAbetaPs, with a low identity to the epitope recognized by the antibody. The prevalent labeling of the beta-layers in lepidosaurian epidermis and of the corneous layer in turtle and crocodilian epidermis suggest that this antibody is mainly directed toward KAbetaPs rich in glycine. The latter are main constituents of the corneous layer in turtles and crocodilians and of the beta-layer in lizards, snakes and the tuatara. These proteins are largely responsible for the inflexibility, mechanical resistance, chromophobicity and relative hydrophobicity of the reptilian corneous layer.