Ceramidase activity in porcine epidermis.

This report presents the first demonstration of a ceramide-hydrolyzing activity in mammalian epidermis. An assay using fractions derived from porcine epidermis and synthetic [3H]ceramide is described, and it is shown that under the conditions used, the Km for ceramide is 110 microM and hydrolysis is linear for up to 2 h. The enzyme activity is maximal at pH 8-9. The specific activity of ceramide hydrolase decreases as the protein concentration in the assay mixture increases, suggesting the possibility of a dissociable inhibitor. Also, the activity can be inhibited by added palmitic acid. Ceramide hydrolysis may be an important regulatory mechanism in the epidermis due to the ability of the liberated free sphingosine to modulate the activity of protein kinase C.