Starch synthase III from Arabidopsis thaliana contains an N-terminal
region, including three in-tandem starch-binding domains, followed by a
C-terminal catalytic domain. We have reported previously that starch-bind-ing domains may be involved in the regulation of starch synthase III func-tion.
Starch deﬁnes a semicrystalline polymer made of two diﬀerent polysaccharide fractions. The A- and B-type crystalline lattices deﬁne the distinct structures reported in cereal and tuber starches, respectively. Amylopectin, the major fraction of starch, is thought to be chieﬂy responsible for this semicrystalline organization while amylose is generally considered as an amorphous polymer with little or no impact on the overall crystalline organization.
In plants and green algae, several starch synthase isozymes are responsible
for the elongation of glucan chains in the biosynthesis of amylose and amy-lopectin. Multiple starch synthase isozymes, which are classified into five
major classes (granule-bound starch synthases, SSI, SSII, SSIII, and SSIV)
according to their primary sequences, have distinct enzymatic properties.
Research in starch biosynthesis is likely to have a great impact on agriculture
and industry in coming years. Although the original purpose of research
into starch synthesis was not industrial application, it is an example of how
science, while trying to answer fundamental questions, may lead to the
manipulation of nature for beneficial purposes.
Although the basic studies of starch synthesis were carried out in England
during the 1940s, and led to the discovery of phosphorylase and Q-enzyme
(branching enzyme), the basis of our modern ideas originated in Argentina
from the work of Luis F.