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Biochemical Characterization of Wild-Type and Mutant Isoamylases of Chlamydomonas reinhardtii Supports a Function of the Multimeric Enzyme Organization in Amylopectin Maturation1
Chlamydomonas reinhardtii mutants of the STA8 gene produce reduced amounts of high amylose starch and phytoglycogen. In contrast to the previously described phytoglycogen-producing mutants of C. reinhardtii that contain no residual isoamylase activity, the sta8 mutants still contained 35% of the nor...
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Published in: | Plant physiology (Bethesda) 2001-04, Vol.125 (4), p.1723-1731 |
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Main Authors: | , , , , , , , , , , |
Format: | Article |
Language: | English |
Online Access: | Get full text |
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Summary: | Chlamydomonas reinhardtii
mutants of the
STA8
gene produce reduced amounts of high amylose starch
and phytoglycogen. In contrast to the previously described
phytoglycogen-producing mutants of
C. reinhardtii
that
contain no residual isoamylase activity, the
sta8
mutants still contained 35% of the normal amount of enzyme activity.
We have purified this residual isoamylase and compared it with the
wild-type
C. reinhardtii
enzyme. We have found that the
high-mass multimeric enzyme has reduced its average mass at least by
one-half. This coincides with the disappearance of two out of the three
activity bands that can be seen on zymogram gels. Wild-type and mutant
enzymes are shown to be located within the plastid. In addition, they
both act by cleaving off the outer branches of polysaccharides with no
consistent difference in enzyme specificity. Because the mutant enzyme
was demonstrated to digest phytoglycogen to completion in vitro, we
propose that its inability to do so in vivo supports a function of the
enzyme complex architecture in the processing of pre-amylopectin
chains. |
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ISSN: | 0032-0889 1532-2548 |