Granule-bound enzyme

The solubilized granule-bound enzymes showed A/, values for ADP-Glc about 10-fold lower than that measured before solubilization (0.96 mmol U for the intact granule activity unpublished results). The granule-bound enzyme is also active with UDP-Glc with 1 mmol 1 UDP-Glc having about 7% of the activity rate seen with 1 mmol ADP-Glc. If the concentration of UDP-Glc is raised to 20 mmol then the rate of activity is about 73% of that of ADP-Glc. Upon solubilization with a-amylase and glucoamylase, activity with... 

The polymerase can occur in either a soluble (hydrophilic) or a granule-bound (hydrophobic) form, depending on prevailing conditions of life. During growth under carbon substrate limitation, the enzyme exists mainly in the soluble state, and after transfer to nutrient-limiting conditions, e.g., ammonium limitation, the granule-associated polymerase appears (for review see [25]). 

Isozymes of plant starch synthases (2, 16-20) and branching enzymes (2, 16, 21-26) have been characterized. Presumably, they play distinct roles in amylopectin and amylose synthesis. Also, plant and Chlamydomonas reinhardtii granule-bound starch synthases (27-33) are responsible for synthesis of amylose. Mutants defective in this enzyme are known as waxy mutants and contain starch granules that have little or no amylose. 

Proteins, particularly granule-bound starch synthesis enzymes entrapped in dried starch granules, are also involved in the determination of the starch-pasting characteristics, even when they are present at less than 0.2% in dried starch. Figure... 

Genetically modiHed (anti-GBSS) potato. Potato starch consists of two components amylose (20%) and amylopectin (80%). Granule-bound starch synthase (GBSS) is the major enzyme involved in the formation of amylose. 

A C. reinhardtii mutant lacking D-enzyme activity has been characterized and has been shown to have significantly lower levels of starch. Other enzymes involved in starch metabolism such as ADP-Glc PPase, granule-bound and soluble starch synthase, BE, phosphorylase, a-glucosidase, amylases, and debranching enzyme activities were not affected. The starch content in the mutant was about 6-13% of wild type and there was an excessive accumulation of maltooligosaccharides up to a polymer size of 16 glucose units. 

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