Biosynthetic relationship between cytosol and membranous dipeptidyl peptidase IV from the rat submandibular gland

• Published in: Japanese Journal of Oral Biology Vol. 25; no. 4; pp. 1168 - 1173
• Main Authors: Fukasawa, Kayoko M., Fukasawa, Katsuhiko, Harada, Minoru
• Format: Journal Article
• Language: English; Japanese
• Published: Japanese Association for Oral Biology 1983
• Subjects: biosynthesis; dipeptidyl peptidase IV; rat; submandibular gland
• ISSN: 0385-0137
• DOI: 10.2330/joralbiosci1965.25.1168

Two forms of dipeptidyl peptidase (DPP) IV purified by immunoaffinity chromatography from the cytosol and Triton X-100-solubilized particulate fractions of rat submandibular gland were shown to have the same Km values and molecular weights as estimated by the two methods of SDS-polyacrylamide gel electrophoresis and density gradient ultracentrifugation, but different pI values (cytosol DPP IV, 5.1; membranous, 4.8). The two forms of DPP IV were bound completely to concanavalin A-Sepharose but showed different elution patterns with α-methyl mannoside. To study the biosynthetic relationship between the two forms, radioactive leucine and fucose were incorporated into these enzymes in vitro and counted by use of specific immunoprecipitation. Incorporation of [14C]leucine into cytosol DPP IV increased in parallel to that of the membranous enzyme during 1 h of incubation. On the contrary, cytosol DPP IV was not labelled with [3H]fucose, whereas its incorporation into the membranous enzyme increased during a 2h incubation period. Therefore, cytosol and membranous DPP IV do not have different functions at their active sites but are heterogeneous glycoproteins; especially the carbohydrate modification process of the two forms of the enzyme is different. Hence, it is suggested that cytosol DPP IV is neither a precursor nor a product of the membranous enzyme.