Abstract
In higher plants several isoforms of starch synthase contribute to the extension of glucan chains in the synthesis of starch. Different isoforms are responsible for the synthesis of essentially linear amylose chains and branched, amylopectin chains. The activity of granule-bound starch synthase I from potato has been compared with that of starch synthase II from potato following expression of both isoforms in Escherichia coli. Significant differences in their activities are apparent which may be important in determining their specificities in vivo. These differences include affinities for ADPglucose and glucan substrates, activation by amylopectin, response to citrate, thermosensitivity and the processivity of glucan chain extension. To define regions of the isoforms determining these characteristic traits, chimeric proteins have been produced by expression in E. coli. These experiments reveal that the C-terminal region of granule-bound starch synthase I confers most of the specific properties of this isoform, except its processive elongation of glucan chains. This region of granule-bound starch synthase I is distinct from the C-terminal region of other starch synthases. The specific properties it confers may be important in defining the specificity of granule-bound starch synthase I in producing amylose in vivo.
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Claims 3
Claim · model-written summary
Potato granule-bound starch synthase I and starch synthase II differed significantly in substrate affinities, amylopectin activation, citrate response, thermosensitivity, and chain-extension processivity.
- Taxon
- potato
Solanum tuberosumt0 - Gene
- granule-bound starch synthase Ie1
- Outcome
- affinities for ADPglucose and glucan substrates, activation by amylopectin, response to citrate, thermosensitivity and the processivity of glucan chain extensione0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Significant differences in their activities are apparent which may be important in determining their specificities in vivo. These differences include affinities for ADPglucose and glucan substrates, activation by amylopectin, response to citrate, thermosensitivity and the processivity of glucan chain extension.”
t0“potato”
e1“The activity of granule-bound starch synthase I from potato has been compared with that of starch synthase II from potato”
Claim · model-written summary
The C-terminal region of granule-bound starch synthase I conferred most isoform-specific properties except processive glucan-chain elongation.
- Taxon
- potatoSolanum tuberosumt0
- Gene
- granule-bound starch synthase Ie0
- Outcome
- most of the specific properties of this isoforme0
- Qualifier
- except its processive elongation of glucan chainse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“These experiments reveal that the C-terminal region of granule-bound starch synthase I confers most of the specific properties of this isoform, except its processive elongation of glucan chains.”
t0“potato”
Claim · model-written summary
The C-terminal region of potato granule-bound starch synthase I differed from that of other starch synthases.
- Taxon
- potatoSolanum tuberosumt0
- Gene
- granule-bound starch synthase Ie0
- Outcome
- distinct from the C-terminal region of other starch synthasese0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“This region of granule-bound starch synthase I is distinct from the C-terminal region of other starch synthases.”
t0“potato”