Substrate Specificity and Primary Structure of Sugar Beet α-Glucosidase

概要

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Sugar beet α-glucosidase exhibits the highest hydrolytic activity, among α-glucosidases, towards soluble starch. α-Glucosidases including sugar beet enzyme produce α-anomeric compounds from maltotriose, soluble starch, phenyl α-maltoside, D-glucal, D-gluco-octenitol and α-glucosyl fruoride. These enzymes, therefore, are not glucoamylases. Conduritol B epoxide (CBE), an affinity labeling reagent, inactivated sugar beet α-glucosidase following pseudo-first-order kinetics. Analyzing an <SUP>3</SUP>HCBE-labeled peptide indicated that the active site sequence was-DGIWIDMNE-. The cDNA (3056 bp), cloned from a library constructed from mRNA of suspension cultured cells, had an open reading frame encoding a polypeptide of 913 amino acid residues. The deduced amino acid sequence contained the active site region determined by CBE modification, and showed a high homology to those from spinach (68%) and barley (55%) α-lucosidases. The primary structure is discussed in relation to some α-amylases.
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