Chapter 1 – Starch Metabolism

Publisher Summary This chapter provides an outline of starch metabolism, overviews the genetics of starch accumulation and mobilization and focuses on those mutants for which clear biochemical defects have been unravelled. Physiology of starch storage is introduced in which circadian clock control, pyrenoidal starch synthesis and hydrogen production are covered briefly. Finally, a renewed interest in fermentative metabolism linked to the production of hydrogen gas has revived an interest in the synthesis and mobilization of the starch energy stores required for this process. The characterization of mutants of GBSSI, the enzyme responsible for amylose synthesis, suggested that GBSSI is an important contributor to amylopectin synthesis. The subsequent characterization of Chlamydomonas mutants defective for one plastidial form of starch phosphorylase provided the first in vivo evidence for a function of this enzyme in starch metabolism. The isolation of other Chlamydomonas mutants strongly suggested the presence of an active heteromultimeric isoamylase whose quaternary structure defined an important component of the polysaccharide aggregation mechanism. Explaining the major differences between the synthesis of glycogen and starch is the “holy grail” of starch research. This may provide the future basis for the development of approaches in green algae concerning the regulation of this important pathway.