alpha-Amylase expressed in human liver is encoded by the AMY-2B gene identified in tumorous tissues

Background: An alpha -Amylase in human liver is detected with an anti-human salivary amylase antibody, but the enzyme activity is very low. We previou sly found that the rat liver contained an amylase which differed from the e nzyme of mice. In this study, we characterized the human liver amylases bio chemically and immunohistochemically. Methods and Results: Although the amy lase activity of human liver was much lower than that of rat, protein moiet y and sugar chains of the human amylase were identified as similar to the r at liver enzyme with an anti-human salivary amylase antibody and by concana valin A (Con A) affinity chromatography. Liver amylases from human and rat were the same size, 50 kDa, on Western blot analysis and had the same isoel ectric points. The cytoplasm of hepatocytes was moderately stained immunohi stochemic ally with the anti-human salivary amylase antibody. Intrahepatic bile ducts were also stained weak-to-moderately. RT-PCR, with a specific pr imer for the consensus sequence of human amylases, amplified a single 474-b p product from the human liver total RNA. The PCR product was sequenced and referred to the homology. Thirteen bases in the 434-bp fragment of the hum an liver amylase differed from the corresponding region of the AMY-I gene t ranscript and the deduced amino acid sequence differed at five residues. Th e human liver amylase cDNA sequence was identical to the corresponding cDNA of the AMY-2B, which was known to expressed in tumorous tissues. In situ h ybridization revealed the expression of AMY-2B mRNA in non-tumorous human l iver. Conclusions: The present results suggest the possibility that a novel amylase detected in tumorous tissues and encoded by the AMY-2B gene is a l iver-specific amylase expressed in the human liver. (C) 2001 Elsevier Scien ce B,V. All rights reserved.