IUBMB Enzyme Nomenclature


Accepted name: 1,3-α-isomaltosidase

Reaction: cyclobis-(1→6)-α-nigerosyl + 2 H2O = 2 isomaltose (overall reaction)
(1a) cyclobis-(1→6)-α-nigerosyl + H2O = α-isomaltosyl-(1→3)-isomaltose
(1b) α-isomaltosyl-(1→3)-isomaltose + H2O = 2 isomaltose

Systematic name: 1,3-α-isomaltohydrolase (configuration-retaining)

Comments: The enzyme, characterized from the bacteria Bacillus sp. NRRL B-21195 and Kribbella flavida, participates in the degradation of starch. The cyclic tetrasaccharide cyclobis-(1→6)-α-nigerosyl is formed from starch extracellularly and imported into the cell, where it is degraded to glucose.

Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, PDB, CAS registry number:


1. Kim, Y.K., Kitaoka, M., Hayashi, K., Kim, C.H. and Cote, G.L. Purification and characterization of an intracellular cycloalternan-degrading enzyme from Bacillus sp. NRRL B-21195. Carbohydr. Res. 339 (2004) 1179-1184. [PMID: 15063208]

2. Tagami, T., Miyano, E., Sadahiro, J., Okuyama, M., Iwasaki, T. and Kimura, A. Two novel glycoside hydrolases responsible for the catabolism of cyclobis-(1→6)-α-nigerosyl. J. Biol. Chem. 291 (2016) 16438-16447. [PMID: 27302067]

[EC created 2017]

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