Starch synthases

Soluble oil metal-working fluids, 1 22 Soluble oils, 15 240 Soluble silicates, 22 451-452 dissolution of, 22 455-456 history and applications of, 22 452 Soluble starch synthases, 12 492 Soluble titanium glycolate complexes, 25 87 Solute clearances... 

Starch soils, 10 285 Starch-splitting enzymes, 10 302 Starch succinates, 4 721, 724t Starch synthases, 12 492-493... 

Denyer, K., Barber, L. M., Edwards, E. A., Smith, A. M., and Wang, T. L. (1997). Two isoforms of the GBSSl class of granule bound starch synthase are differently expressed in the pea plant (Pisum sativum L.). Plant, Cell and Environment. 20,1566-1572. 

STARCH SYNTHASE STATE FUNCTION STATIONARY STATE STEADY STATE... 

Each of the two reactive groups (Xa, Xb) at the active site of starch synthase makes a nucleophilic attack on ADP-glucose, displacing ADP and forming a covalent attachment to C-l of the glucose unit. 

Many repetitions of this sequence extend the oligosaccharide, adding glucose residues at its reducing end, with Xa and Xb alternately carrying the growing starch chain. When the chain reaches an appropriate length, it is separated from starch synthase. 

Starch synthase in chloroplasts and amyloplasts catalyzes the addition of single glucose residues, donated by ADP-glucose, to the reducing end of a starch molecule by a two-step insertion mechanism. Branches in amylopectin are introduced by a second enzyme. 

Phytoglycogen-branching enzyme has been found in du however, no phytoglycogen was isolated by Black et al.23 Preiss and Boyer396 reported that the du mutation lowered starch synthase II activity and also lowered branching enzyme Ha activity. Gao et al.397 used a molecular approach to clone the du gene in maize endosperms and, based on amino acid sequence similarity of the predicted protein product with the soluble starch synthase III of potato,398 concluded that du most likely encodes the 180 000 molecular weight, primer-dependent soluble starch synthase described previously.399,400,401... 

Additional characterization of the two major soluble starch synthases in maize endosperm indicated distinct catalytic properties.402 Soluble starch synthase II has been reported to be encoded by the du gene.397 the initially observed reduction in BEIIa is a secondary effect and may be related to protein-to-protein interactions. 

---