The differentiation of the corneous layers of lizard epidermis has been analyzed 
by ultrastructural immunocytochemistry using specific antibodies against 
alpha-keratins and keratin associated beta-proteins (KAbetaPs, formerly 
indicated as beta-keratins). Both beta-cells and alpha-cells of the corneous 
layer derive from the same germinal layer. An acidic type I alpha-keratin is 
present in basal and suprabasal layers, early differentiating clear, 
oberhautchen, and beta-cells. Type I keratin apparently disappears in 
differentiated beta- and alpha-layers of the mature corneous layers. Conversely, 
a basic type II alpha-keratin rich in glycine is absent or very scarce in basal 
and suprabasal layers and this keratin likely does not pair with type I keratin 
to form intermediate filaments but is weakly detected in the pre-corneous and 
corneous alpha-layer. Single and double labeling experiments show that in 
differentiating beta-cells, basic KAbetaPs are added and replace type-I keratin 
to form the hard beta-layer. Epidermal alpha-keratins contain scarce cysteine 
(0.2-1.4 %) that instead represents 4-19 % of amino acids present in KAbetaPs. 
Possible chemical bonds formed between alpha-keratins and KAbetaPs may derive 
from electrostatic interactions in addition to cross-linking through disulphide 
bonds. Both the high content in glycine of keratins and KAbetaPs may also 
contribute to increase the hydrophobicy of the beta- and alpha-layers and the 
resistance of the corneous layer. The increase of gly-rich KAbetaPs amount and 
the bonds to the framework of alpha-keratins give rise to the inflexible 
beta-layer while the cys-rich KAbetaPs produce a pliable alpha-layer.