Starch is an abundant carbohydrate widespread in plants. This high energy polysaccharide is preserved in the storage tissues, such as seeds. In the germination of plant seeds, the starch is degraded by several hydrolytic enzymes (α amylase, β amylase, debranching enzyme and α glucosidase), followed by conversion to the biological materials and energy necessary for growth. 1) In plant seeds, starch exists as practically insoluble polysaccharide called starch granules or raw starch. Therefore, the pathway of starch degradation in the germination stage has been generally considered as follows. 2)α Amylase is a key enzyme attacking the starch granules initially to liberate soluble dextrin. Produced dextrin is hydrolyzed by the further action combined with α amylase, β amylase and debranching enzyme to form oligosaccharides such as maltose. Finally, α glucosidase converts the oligosaccharides to glucose. Among these starch degrading enzymes α amylase has been considered to be the exclusive enzyme capable of hydrolyzing the starch granules, while the other enzymes were not. However, it had been reported that plant α glucosidases exhibited the ability to attack soluble starch effectively, 3,4) which suggested that α glucosidase hydrolyzed not only oligosaccharides such as maltose but starch as well in plant seeds. Recently, barley, 5,6) millet 7,8) and rice 9,10) α glucosidases were found to be capable of degrading the starch granules. The combination of α glucosidase and α amylase exhibited the synergism of degradation of starch granules. 5,6,11) It is of interest to learn the α glucosidase mediated starch metabolism in the germination stage. The first section of this article introduces our molecular level analysis on the degradation of starch granules catalyzed by plant α glucosidase.In the second section, we describe the multiple formation mechanism of rice α glucosidases observed in the ripening and germination stages. α Glucosidases, which are synthesized in the ripening stage and preserved in dry seeds, are important in starch metabolism, since these enzymes hydrolyze starch granules before attacking by α amylase. Certain α glucosidase isozymes, which are expressed in the early stage of germination, also hydrolyze starch granules. It is valuable to learn the expression systems of α glucosidases in the dry seeds and germinating seeds. In both seeds, there were several enzymes, of which the expression feature differed by variety of rice, requiring more precise analysis to understand the contribution of each enzyme to starch metabolism. The second section of this article introduces the mechanism for the formation of rice α glucosidase isoforms and isozymes as well as their characteristics elucidated using purified en- Abstract: In germination of plant seeds, storage starch is principally degraded by the combination of amylolytic enzymes. As starch is an insoluble granule, a conventional view of the degradation pathway is that the initial attack is performed by α-amylase having the starch granule-binding ability. Pla...

Starch derived oligosaccharides such as isomalto and nigero oligosaccharides are usually produced from starch by the combination of hydrolysis and transglucosylation. 1,2) As a first step, starch is liquefied by thermostable α amylase at around 100 C. This gelatinized starch is then cooled to around 50 65 C and hydrolyzed to maltose and maltotriose by β amylase and starch debranching enzymes. α Glucosidase is added and catalyzes the transglucosylation toward maltose and maltotriose to produce glucosidic linkage other than α 1,4 linkage at the non reducing end of maltooligosaccharides. The type of linkage produced is dependent on the specificity of α glucosidase for the glucosidic linkage. For example, α glucosidases from Aspergillus niger (ANG) and Acremonium strictum (ASG) produce isomalto (α 1,6 linkage) and nigero (α 1,3 linkage) oligosaccharides, respectively.3,4) These enzymes are utilized in industrial oligosaccharide production.The degree of polymerization (DP) of these oligosaccharides is usually 2 4. This is because the substrate for transglucosylation is mainly maltose and maltotriose produced from starch by β amylase. It is very difficult to introduce glucosidic linkage other than α 1,4 linkage at the non reducing end of longer maltooligosaccharides by the usual hydrolysis transglucosylation process because long maltooligosaccharides are immediately insoluble in water due to retrogradation. In addition, it is very difficult to produce long maltooligosaccharides efficiently with no production of short maltooligosaccharides by α amylase since this enzyme produces short maltooligosaccharides even in the initial stages of starch degradation.Cyclodextrin glucanotransferase (CGTase), which is a type of glycosyl transferase belonging to glycoside hydrolase family 13, 5,6) produces CDs from starch via intramolecular transglycosylation.7) This enzyme is known to catalyze four reactions: (i) CD production, (ii) transglycosylation of maltooligosaccharides to other maltooligosaccharides (disproportionation), (iii) the opening of circular CDs and the subsequent transfer to maltooligosaccharides (coupling), and (iv) hydrolysis.7) The hydrolytic activity of CGTase is generally lower than the transglycosylation activity.7) CGTase are thought to degrade starch more mildly than α amylase and CGTase is an appropriate enzyme to produce long maltooligosaccharides from starch.The sweetness of the starch derived glucan generally depends on its chain length. Shorter chain length glucans have a stronger sweetness than longer chain glucans. Although the sweetness of long chain glucans is weak, these substances are capable of masking the bitter tastes of foods and beverages and providing a rich taste. Abstract: The isomalto-and nigero-oligosaccharides are usually produced from starch by the combination of α-glucosidase and starch degrading enzymes, such as α-and β-amylases. In this study, a new reaction system for the production from starch of two α-1,4 glucans having α-1,6-and α-1,3-linked glucosyl residues at or near the non-...

Cyclodextrin (CD) has a closed ring structure consisting of D glucose residues linked through α (1,4) linkages. The most common CDs consist of six, seven, or eight glucose residues, and are named α , β and γ CD, respectively. CDs have a hydrophilic outer surface and a relatively hydrophobic internal cavity. CDs are able to form complexes with various molecules. The formation of complexes leads to changes in the chemical and physical properties of the molecule including stability and solubility; thus there have been extensive applications of CDs in the food, cosmetic, agricultural and pharmaceutical industries. 1) Cyclodextrin glucanotransferase (CGTase; EC 2.4.1.19) forms CDs from starch and related α (1,4) linked glucose polymers through intramolecular transglycosylation. 2) This enzyme belongs to glycoside hydrolase family 13 (α amylase family), based on its amino acid sequence. 3 5) Members of this family show various reaction specificities but have the following common features: a (β α)8 barrel structure and four highly conserved regions, regions I IV, in the primary sequence. The conserved regions include invariant catalytic residues, two Asp residues and one Glu residue, and other amino acids involved in transition state stabilization. 3) A number of bacteria and archaea (e.g., Bacillus, Thermoanaerobacter and Thermococcus species) have been isolated as CGTase producers. 6) Many studies on X ray crystallographic structures of CGTases complexed with substrates, products, and inhibitors have revealed that CGTase possesses a substrate binding groove that accommodates at least 7 glucose residues at the donor subsites and 3 at the acceptor subsites (subsite −7 to +3), and contains an aromatic amino acid in a dominant position at the center of the substrate binding groove. 2,7 9) As all known CGTases produce a mixture of CDs, they are subdivided into α , β and γ CGTases based on the major CD product. The majority of CGTases reported are β CGTases while α and γ CGTases are less frequent. γ CD is the most expensive CD due to the low yield of this substance from the current CGTases. Several attempts have been made to enhance the γ CD yield, but no satisfactory results have been obtained to date. 10,11) In addition to the ability of CD synthesis (cyclization reaction), CGTase catalyzes three other reactions: coupling, disproportionation and starch hydrolysis. In the coupling reaction, CD is cleaved and transferred to an acceptor substrate. In the disproportionation reaction and starch hydrolysis reaction, a linear maltooligosaccharide is cleaved and then glycosyl residue transfers to another linear substrate and water, respectively. Thus CGTase is also utilized for the synthesis of glycosides. 12,13) Cyclodextrinase (CDase; EC 3.2.1.54) hydrolyzes CDs much faster than starch and pullulan. 14) Many CDases have been isolated from various bacteria, including Alicy- Abstract: The alkaliphilic soil bacterium Bacillus clarkii 7364 was found to produce cyclodextrin glucanotransferase (CGTase), an enzyme which conver...