A low-molecular-weight soluble protein from bovine lingual epithelium. II. Purification and characterization.

In an earlier study of rat lingual epithelium, we examined the total SDS-soluble protein from epithelia isolated at different states of development by polyacrylamide gel electrophoresis. In this study, rather than work with total SDS-soluble proteins, we have carried out a series of sequential extractions of bovine lingual epithelium. To separate epithelium from connective tissue, slices of dorsal tongue mucosa were incubated in a solution containing EDTA and 4 proteolytic enzyme inhibitors. We have isolated and partially characterized a low-molecular-weight (LMW) protein from the phosphate-buffered saline extract of bovine lingual epithelium. In the work reported here, we describe some of the biochemical and immunologic characteristics of this protein. The bovine lingual LMW protein has a molecular weight of 8700 +/- 450, an isoelectric point of 4.7 +/- 0.2 pH units, and a high content of the acidic amino acids aspartate and glutamate. We prepared an antibody to LMW protein and examined its specificity by a microenzyme-linked immunosorbant assay (ELISA). We found that the antibody to LMW protein reacts very strongly against LMW protein while it exhibits no cross-reactivity with low levels of an authentic keratin protein but moderate cross-reactivity at higher concentrations of this authentic keratin protein. In a previous publication we have reported the immunohistochemical localization and distribution of this LMW protein.