シュードモナス細菌のイソアミラーゼとマルトテトラオース生成アミラーゼの一次構造と遺伝子発現
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概要
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Isoamylase and maltotetraose-forming amylase (G_4-amylase) produced by Pseudomonas are important enzymes in the starch industry. The isoamylase hydrolyzes branching points with α-1,6-glucosidic linkages in amylopectin and glycogen, and produces linear maltodextrins. The G_4-amylase catalyzes the release of α-maltotetraose exoglycolytically from the nonreducing ends of starch, whereas other exo-type amylases (glucoamylase and β-amylase) release β-anomeric products by exoglycolytic cleavage, and α-amylase hydrolyzes starch endoglycolytically to produce α-malto-oligosaccharides. Thus, the G_4-amylase has unique activity for hydrolysis of starch intermediate between those of α-amylase and β-or glucoamylase. For understanding the molecular basis of the unique action mechanism of isoamylase and G_4-amylase and also for elucidating the regulation of the syntheses of these enzymes, we determined the nucleotide sequences of these genes and examined the regulation of these gene expressions. The isoamylase was consisted of 771 amino acids which contained 26 residues as a signal peptide. The G_4-amylase was consisted of 547 amino acids which contained 21 residues as a signal peptide. These two amylases contained four sequences conserved in many other amylases. These four sequences probably form a cleft involved in catalytic function and substrate binding. Expressions of the isoamylase gene (iam) and the G_4-amylase gene (amyP) were induced by maltose. The expression of the latter was repressed by glucose at posttranscriptional level, whereas that of the former was not repressed by glucose.
- 福山大学の論文