The necessity of debranching in starch biosynthesis

Although research in starch biosynthesis has been carried out since the 1940s, many issues remain unresolved. For example, the number of reactions in the pathway is still an open question. The biosynthesis of the starch granule from glucose-1-phosphate has long been considered to consist of three steps: 1. The synthesis of a glucosyl donor. 2. The formation of a-1,4 linkages to add the donor to a growing chain. 3. The hydrolysis of an a-1,4 linkage and subsequent formation of an a-1,6 linkage to introduce a branch point. Recently, a fourth step has been proposed in starch granule biosynthesis (Ball et al., 1996). This step involves the hydrolysis of a-1,6 linkages by the action of a debranching enzyme. Our study provides further evidence for the necessity of this debranching step through the analysis of the production of phytoglycogen and other novel polysaccharides in strains of Chlamydomonas reinhardtii lacking isoamylase activity. We demonstrate that granule-bound starch synthase I (GBSS I) is necessary to synthesize the minute amounts of novel insoluble amylose-like materials found in these mutants, and can do so in an unbound form. We also show that crystalline amylopectin is necessary for granule binding of GBSS I.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Biology.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

1999

Author dc:creator

• Shaw, Eudean

Advisor dc:contributor.advisor

• Anthony J. Sinskey.

• Biology.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/29739

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/29739