title: Comprehensive enzymatic analysis of the amylolytic system in the digestive fluid of the sea hare, Aplysia kurodai: Unique properties of two α-amylases and two α-glucosidases.
abstract: Sea lettuce (Ulva pertusa) is a nuisance species of green algae that is found all over the world. East-Asian species of the marine gastropod, the sea hare Aplysia kurodai, shows a clear feeding preference for sea lettuce. Compared with cellulose, sea lettuce contains a higher amount of starch as a storage polysaccharide. However, the entire amylolytic system in the digestive fluid of A. kurodai has not been studied in detail. We purified α-amylases and α-glucosidases from the digestive fluid of A. kurodai and investigated the synergistic action of these enzymes on sea lettuce. A. kurodai contain two α-amylases (59 and 80 kDa) and two α-glucosidases (74 and 86 kDa). The 59-kDa α-amylase, but not the 80-kDa α-amylase, was markedly activated by Ca(2+) or Cl(-). Both α-amylases degraded starch and maltoheptaose, producing maltotriose, maltose, and glucose. Glucose production from starch was higher with 80-kDa α-amylase than with 59-kDa α-amylase. Kinetic analysis indicated that 74-kDa α-glucosidase prefers short α-1,4-linked oligosaccharide, whereas 86-kDa α-glucosidase prefers large α-1,6 and α-1,4-linked polysaccharides such as glycogen. When sea lettuce was used as a substrate, a 2-fold greater amount of glucose was released by treatment with 59-kDa α-amylase and 74-kDa α-glucosidase than by treatment with 45-kDa cellulase and 210-kDa β-glucosidase of A. kurodai. Unlike mammals, sea hares efficiently digest sea lettuce to glucose by a combination of two α-amylases and two α-glucosidases in the digestive fluids without membrane-bound maltase-glucoamylase and sucrase-isomaltase complexes.
authors.affiliation: Department of Biological Science and Technology, The University of Tokushima Graduate School, 2-1 Minamijosanjima, Tokushima 770-8506, Japan.
authors.forename: Akihiko
authors.initials: A
authors.lastname: Tsuji
authors.affiliation: Department of Biological Science and Technology, The University of Tokushima Graduate School, 2-1 Minamijosanjima, Tokushima 770-8506, Japan.
authors.forename: Nami
authors.initials: N
authors.lastname: Nishiyama
authors.affiliation: Department of Biological Science and Technology, The University of Tokushima Graduate School, 2-1 Minamijosanjima, Tokushima 770-8506, Japan.
authors.forename: Miki
authors.initials: M
authors.lastname: Ohshima
authors.affiliation: Department of Biological Science and Technology, The University of Tokushima Graduate School, 2-1 Minamijosanjima, Tokushima 770-8506, Japan.
authors.forename: Saori
authors.initials: S
authors.lastname: Maniwa
authors.affiliation: Department of Biological Science and Technology, The University of Tokushima Graduate School, 2-1 Minamijosanjima, Tokushima 770-8506, Japan.
authors.forename: Shuji
authors.initials: S
authors.lastname: Kuwamura
authors.affiliation: Department of Biological Science and Technology, The University of Tokushima Graduate School, 2-1 Minamijosanjima, Tokushima 770-8506, Japan.
authors.forename: Masataka
authors.initials: M
authors.lastname: Shiraishi
authors.affiliation: Department of Biological Science and Technology, The University of Tokushima Graduate School, 2-1 Minamijosanjima, Tokushima 770-8506, Japan.
authors.forename: Keizo
authors.initials: K
authors.lastname: Yuasa
keywords: 4MU-α-Glu, 4-methylumbelliferyl α-glucoside; ApAGL74, Aplysia 74-kDa α-glucosidase; ApAGL86, Aplysia 86-kDa α-glucosidase; ApAmy59, Aplysia 59-kDa α-amylase; ApAmy80, Aplysia 80-kDa α-amylase; CMC, carboxymethylcellulose; GHF, glycoside hydrolase family; PVDF, polyvinylidene fluoride; Sea hare; Sea lettuce; TLC, thin layer chromatography; α-Amylase; α-Glucosidase