Differentiation of Novel Human α-Amylase from Salivary and Pancreatic α-Amylases

yHXA is the gene product of a newly found human a-amylase gene (AMY2B) expressed in yeast. Its mode of action on a derivative of p-nitrophenyl ƒ¿-maltopentaoside, FG5P (FG-G-G-GG-P), was compared with those of the ƒ¿-amylases (yHSA, yHPA), which were produced by expression of human salivary and pancreatic ƒ¿-amylase genes (AMY1 , AMY2A) in yeast. The product analysis of the digests by HPLC showed that the enzymes hydrolyzed FG5P to FG3 (FG-G-G) and p-nitrophenyl a-maltoside (G-G-P) and to FG4 (FG-G-G-G) and p-nitrophenyl ƒ¿-glucoside (G-P) , and the ratio of the two reactions changed with pH. The three enzymes differed from each other in the mode of action at pH 5.5. The molar ratio of FG4 to FG3 in the digest with yHXA was the largest and that with yHSA was the least.