Title : Electrophoretic characterization of posttranslational modifications of human parotid
salivary alpha-amylase
Abstract :
- Human salivary alpha-amylase displays multiple bands upon native polyacrylamide gel electrophoresis
- In fresh saliva, due to posttranslational modifications, a pattern of 5-6 isozymes is observed
- The isozymes are designated 1-6, in the order of increasing anodal mobility
- As a result of the development of a rapid and sensitive electrophoresis system, with markedly higher resolution than previously reported, we concluded that a previously proposed model (Karn et al., Biochem
- Genet
- 1973, 10, 341-350) is inadequate to explain the origin of the various bands
- We propose an alternative model that fits in with our new and previously made observations
- According to this model, band 2 is the primary gene product and band 1 is its glycosylated counterpart--with only one neutral oligosaccharide present on each molecule
- Band 3 originates from band 1 by the transialidase-catalyzed incorporation of sialic acid into the biantennary chain
- Bands 4 and 6 originate from bands 2 and 4, respectively, by deamidation; band 5 is the deamidation product of amylase with an acidic oligosaccharide (band 3)
- Only a minor part of band 3 consists of the deamidation product of band 1
- Peptide Asn-Gly-Ser ( residues 427-429 ) is the most probable candidate for glycosylation; literature data suggests that deamidation occurs in the stretch Glu-Asn-Gly-Lys-Asp ( residues 364-368 ) and Asn-Gly-Asn-Cys ( residues 474-477 )
- Both glycosylation and deamidation might play a role in the clearance of amylase from the systemic circulation
- The electrophoresis system described is a powerful tool to determine amylase isozyme distributions in health and disease, especially for the screening of alterations seen in ectopically produced amylase