Molecular Structure of Glycogen in Escherichia coli.

Glycogen, a randomly branched glucose polymer, provides energy storage in organisms. It forms small ß particles which in animals bind to form composite α particles, which give better glucose release. Simulations imply ß particle size is controlled only by activities and sizes of glycogen biosynthetic enzymes and sizes of polymer chains. Thus, storing more glucose requires forming more ß particles, which are expected to sometimes form α particles. No α particles have been reported in bacteria, but the extraction techniques might have caused degradation. Using milder glycogen extraction techniques on Escherichia coli, transmission electron microscopy and size-exclusion chromatography showed α particles, consistent with this hypothesis for α-particle formation. Molecular density and size distributions show similarities with animal glycogen, despite very different metabolic processes. These general polymer constraints are such that any organism which needs to store and then release glucose will have similar α and ß particle structures: a type of convergent evolution.

Improved understanding of rice amylose biosynthesis from advanced starch structural characterization.

BACKGROUND: It has been shown from the chain length distributions (CLDs) that amylose chains can be divided into at least two groups: long and short amylose chains. These molecular structures influence some functional properties of starch, such as digestibility and mouth-feel. GBSSI is the key enzyme for the elongation of amylose chains; however, the effect of other starch biosynthesis enzymes in amylose synthesis is still not fully understood. Two advanced starch characterization techniques, size exclusion chromatography (SEC) and fluorophore-assissted carbohydrate electrophoresis (FACE), together with a newly developed starch biosynthesis model, are used to improve understanding of amylose biosynthesis. RESULTS: SEC and FACE were used to determine the CLD of amylose and amylopectin in various native and mutant rice starches. The types of starch branching enzymes (SBEs) involved in the synthesis of the distinct features seen for shorter degrees of polymerization, DP, < 2000, and longer (DP > 2000) amylose chains are identified by combining these data with a mathematical model of amylopectin biosynthesis. The model enables each feature in the amylopectin CLD to be parameterized in terms of relative SBE activities, which are used to explain differences in the genotypes. CONCLUSIONS: The results suggest that while GBSSI is the predominant enzyme controlling the synthesis of longer amylose chains, some branching enzymes (such as BEI and BEIIb) also play important roles in the synthesis of shorter amylose chains.