tailieunhanh - Báo cáo Y học: Comparison of starch branching enzyme I and II from potato

The in vitro activities of purified potato starch branching enzyme (SBE) I and II expressed in Escherichia coli were compared using several assay methods. With the starch– iodine method, it was found that SBE I was more active than SBE II on an amylose substrate, whereas SBE II was more active than SBE I on an amylopectin substrate. Both enzymes were stimulated by the presence of phosphate. On a substrate consisting of linear dextrins (chain length 8–200 glucose residues), no significant net increase in molecular mass was seen on gel-permeation chromatography after incubation with the enzymes. This indicates intrachain branching. | Eur. J. Biochem. 268 6140-6145 2001 FEBS 2001 Comparison of starch branching enzyme I and II from potato Ulrika Rydberg1 Lena Andersson2 Roger Andersson2 Per Aman2 and Hakan Larsson1 1 Department of Plant Biology and Department of Food Science Swedish University of Agricultural Sciences Uppsala Sweden The in vitro activities of purified potato starch branching enzyme SBE I and II expressed in Escherichia coli were compared using several assay methods. With the starchiodine method it was found that SBE I was more active than SBE II on an amylose substrate whereas SBE II was more active than SBEI on an amylopectin substrate. Both enzymes were stimulated by the presence of phosphate. On a substrate consisting of linear dextrins chain length 8-200 glucose residues no significant net increase in molecular mass was seen on gel-permeation chromatography after incubation with the enzymes. This indicates intrachain branching of the substrate. After debranching of the products the majority of dextrins with a degree of polymerization dp greater than 60 were absent for SBE I and those with a dp greater than 70 for SBE II. To study the shorter chains the debranched samples were also analysed by high-performance anion-exchange chromatography. The products of SBE I showed distinct populations at dp 11-12 and dp 29-30 whereas SBE II products had one broader population with a peak at dp 13 - 14. An accumulation of dp 6 - 7 chains was seen with both isoforms. Keywords gel-permeation chromatography GPC high-performance anion-exchange chromatography HPAEC Solanum tuberosum starch branching enzyme starch. Starch is composed of linear and branched chains of a-D-glucose residues. The starch branching enzymes EC which are responsible for forming a-1 6-linkages in the glucan can be divided into two classes class A . potato and maize SBE II pea SBE I and class B . potato and maize SBE I pea SBE II . The A and B isoforms have highly similar amino-acid sequences but usually .