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  - Compart, Julia
A1  - Li, Xiaoping
A1  - Fettke, Jörg
T1  - Starch-A complex and undeciphered biopolymer
JF  - Journal of plant physiology : biochemistry, physiology, molecular biology and biotechnology of plants
N2  - Starch is a natural storage carbohydrate in plants and algae. It consists of two relatively simple homo-biopolymers, amylopectin and amylose, with only alpha-1,4 and alpha-1,6 linked glucosyl units. Starch is an essential source of nutrition and animal food, as well as an important raw material for industry. However, despite increasing knowledge, detailed information about its structure and turnover are largely lacking. In the last decades, most data were generated using bulk experiments, a method which obviously presents limitations regarding a deeper understanding of the starch metabolism. Here, we discuss some unavoidable questions arising from the existing data. We focus on a few examples related to starch biosynthesis, degradation, and structure where these limitations strongly emerge. Closing these knowledge gaps will also be extremely important for taking the necessary steps in order to set up starch-providing crops for the challenges of the ongoing climate changes, as well as for increasing the usability of starches for industrial applications by biotechnology.
KW  - Starch
KW  - Starch structure
KW  - Organization model
KW  - Starch metabolism
KW  - Analytical limitations
Y1  - 2021
U6  - https://doi.org/10.1016/j.jplph.2021.153389
SN  - 0176-1617
SN  - 1618-1328
VL  - 258
SP  - 258
EP  - 259
PB  - Elsevier
CY  - München
ER  -