TY  - JOUR
A1  - Nakamura, Yasunori
A1  - Ono, Masami
A1  - Utsumi, Chikako
A1  - Steup, Martin
T1  - Functional interaction between plastidial starch phosphorylase and starch branching enzymes from rice during the synthesis of branched maltodextrins
JF  - Plant & cell physiology
N2  - The present study established the way in which plastidial alpha-glucan phosphorylase (Pho1) synthesizes maltodextrin (MD) which can be the primer for starch biosynthesis in rice endosperm. The synthesis of MD by Pho1 was markedly accelerated by branching enzyme (BE) isozymes, although the greatest effect was exhibited by the presence of branching isozyme I (BEI) rather than by isozyme IIa (BEIIa) or isozyme IIb (BEIIb). The enhancement of the activity of Pho1 by BE was not merely due to the supply of a non-reducing ends. At the same time, Pho1 greatly enhanced the BE activity, possibly by generating a branched carbohydrate substrate which is used by BE with a higher affinity. The addition of isoamylase to the reaction mixture did not prevent the concerted action of Pho1 and BEI. Furthermore, in the product, the branched structure was, at least to some extent, maintained. Based on these results we propose that the interaction between Pho1 and BE is not merely due to chain-elongating and chain-branching reactions, but occurs in a physically and catalytically synergistic manner by each activating the mutual capacity of the other, presumably forming a physical association of Pho1, BEI and branched MDs. This close interaction might play a crucial role in the synthesis of branched MDs and the branched MDs can act as a primer for the biosynthesis of amylopectin molecules.
KW  - Amylopectin
KW  - Glucan
KW  - Phosphorylase
KW  - Rice
KW  - Starch
KW  - Starch branching enzyme
Y1  - 2012
U6  - https://doi.org/10.1093/pcp/pcs030
SN  - 0032-0781
VL  - 53
IS  - 5
SP  - 869
EP  - 878
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Nakamura, Yasunori
A1  - Ono, Masami
A1  - Sawada, Takayuki
A1  - Crofts, Naoko
A1  - Fujita, Naoko
A1  - Steup, Martin
T1  - Characterization of the functional interactions of plastidial starch phosphorylase and starch branching enzymes from rice endosperm during reserve starch biosynthesis
JF  - Plant science : an international journal of experimental plant biology
N2  - Functional interactions of plastidial phosphorylase (Phol) and starch branching enzymes (BEs) from the developing rice endosperm are the focus of this study. In the presence of both Phol and BE, the same branched primer molecule is elongated and further branched almost simultaneously even at very low glucan concentrations present in the purified enzyme preparations. By contrast, in the absence of any BE, glucans are not, to any significant extent, elongated by Phol. Based on our in vitro data, in the developing rice endosperm, Phol appears to be weakly associated with any of the BE isozymes. By using fluorophore-labeled malto-oligosaccharides, we identified maltose as the smallest possible primer for elongation by Phol. Linear dextrins act as carbohydrate substrates for BEs. By functionally interacting with a BE, Phol performs two essential functions during the initiation of starch biosynthesis in the rice endosperm: First, it elongates maltodextrins up to a degree of polymerization of at least 60. Second, by closely interacting with BEs, Phol is able to elongate branched glucans efficiently and thereby synthesizes branched carbohydrates essential for the initiation of amylopectin biosynthesis.
Y1  - 2017
U6  - https://doi.org/10.1016/j.plantsci.2017.09.002
SN  - 0168-9452
VL  - 264
SP  - 83
EP  - 95
PB  - Elsevier
CY  - Clare
ER  -