COVALENTLY BOUND LIPIDS IN KERATINIZING EPITHELIA

Covalently bound lipids have been identified and compared in keratiniz ing porcine epithelia including epidermis and oral epithelium from pal ate and gingiva. Stratum corneum was isolated by tryptic digestion, an d after extensive extraction of lipids using a series of chloroform-me thanol mixtures, the residual tissue was subjected to alkaline hydroly sis to release covalently bound lipids. The lipids so released were an alyzed by quantitative thin-layer chromatography. Stratum corneum from each of the three anatomical sites contained omega-hydroxyceramides, omega-hydroxyacids and fatty acids. In epidermal stratum corneum the t otal covalently bound lipids represented 2.4% of the dry weight of the tissue, but in the oral epithelia this figure was consistently lower: 0.24% in palatal stratum corneum and 0.20% in gingival stratum corneu m. Transmission electron microscopy before and after lipid extraction confirms the presence of a lipid envelope in epidermal stratum corneum and demonstrates the absence of this structure in oral stratum corneu m.