SENSITIVITY OF DESQUAMIN TO PROTEOLYTIC DEGRADATION

The stratum corneum is both a desquamating and degradative tissue; cell contacts become weaker in the outer lamellae and a variety of proteolytic and glycolytic enzymes cleave many macromolecules into free amino acids and saccharides. We have reported on a 40-kilodalton glycoprotein from human stratum corneum; because of its unique lectin-like properties, we believe that it plays a major role in desquamation and have named it desquamin. If desquamin is to function as a lectin during desquamation, it must survive enzymatic degradation in the outer stratum corneum. Accordingly, we treated this glycoprotein with a number of proteinases and found that desquamin is resistant in vitro to most of the types of proteinases that have been reported in the stratum corneum as well as several others that have not been identified as present in the tissue. In the stratum corneum, the lipids of the intercorneal mortar shield the glycoproteins; hence, desquamin is even less likely to be susceptible to endogenous proteolysis in vivo than in vitro.