Dextranases are enzymes that hydrolyze the α 1,6 glucosyl backbone chain of dextran and isomaltooligosaccharides. Dextranases are classified as endolytic enzymes (endodextranase) or exolytic enzymes (exodextranase) by their reaction modes. Furthermore, dextranases are divided into several families on the basis of the similarity in their amino acid sequences. 1,2) Most endodextranases belong to glycoside hydrolase family (GH) 49 and 66, and exodextranases belong to GH13,15, 27, 49 and 87. 3) The dextranase from Streptococcus mutans ATCC 25175 (SmDex) is an endodextranase (EC 3.2.1.11; 6 α D glucan 6 glucanohydrolase) that is classified under GH66. GH66 enzymes are composed of endodextranase and cycloisomaltooligosaccharide glucanotransferase 4) (EC 2.4.1.248; (1 6) α D glucan:(1 6) α D glucan 6 α D (1 6α D glucano) transferase (cyclizing)). In GH66 members, twenty nine enzymes have been reported and sixteen enzymes have been characterized at present.There are two types of chemical modification reagents based on their inactivation mechanisms, 5) i) two molecules reaction type (Equation (1)) and ii) intermediate formation type (Equation (2)) as follows:where E, R, E R and E R are intact enzyme, chemical modification reagent, inactivated enzyme bound by reagent covalently, and reversible intermediate complex, respectively. In Equation (2), k and KR are the rate constant of irreversible inactivation and dissociation constant of intermediate complex, respectively. Inactivation of the suicide substrate (mechanism based inactivator) follows the intermediate formation type mechanism. 6) Suicide substrate itself is an inert compound that does not attack any free amino acid. When this compound is incorporated into the catalytic site of an enzyme, its inert active species is activated by enzyme reaction to form the covalent linkage with amino acid residue, resulting in the inactivation of the enzyme. 6) Epoxyalkyl based suicide substrate is an effective material to label the catalytic residues and has been applied in a number of glycosidases. 7 17) ω Epoxyalkyl α glucopyranosides have already been reported to show irreversible inhibition to the isomalto dextranase (IMDex) (EC 3.2.1.94; 6 α D glucan isomaltohydrolase) from Arthrobacter globiformis T6 with the suicide substrate mechanism. 18) IMDex is an exodextranase which produces isomaltose from the non reducing terminal of dextran, suggesting a possibility that ω epoxyalkyl α glucopyranoside also becomes a suicide substrate for endodextranase. Therefore, 3 ,4 epoxybutyl α D glucopyranoside (E4G), 4 ,5 epoxypentyl α D glucopyranoside (E5G), and 5 ,6 epoxyhexyl α D J. Appl. Glycosci., 57, 269 272 (2010)
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