Soluble starch synthase

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... 

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. 

Multiple forms of soluble starch synthases are present in barley endosperm,178 pea seeds,43 179 wheat endosperm,180482 maize endosperm,174 183-186 potato tuber,187 189 Arabidopsis,190 rice seed,191 192 Chlamydomonas reinhardtii,m sorghum seeds, teos-inte seeds and spinach leaf (the latter three are reviewed in references 2,7 and 27). 

In further experiments,185 it was found that DU1 was one of the two major soluble starch synthases, and when the C-terminal 450 residues of DU1 were expressed in E. coli, it was shown to have SS activity. Of interest was that antisera prepared against DU1 detected a soluble protein in endosperm extracts of molecular size greater than 200 kDa that was absent in dul mutants.185 The antisera reduced starch synthase activity by 20-30% in kemal extracts. In the same study, antisera prepared against SSI reduced starch synthase activity by 60%. In dul mutants, antisera prepared against SSI reduced the SS activity essentially to zero, suggesting that SSI and SSII were the only maize endosperm soluble starch synthases. Because of the high similarity in sequence of the DU1 starch synthase II to the potato SSIII, and because both are exclusively soluble, it is argued that DU1 is the evolutionary counterpart of potato SSIII.185,188 206 It is proposed that DU1 and maize SSII should be known as maize SSIII.184... 

Antibody prepared against SSI effectively neutralized souble SSI activity, but had no effect on either the activities of GBSSI or GBSSII, or even on SSII. Alternatively, antibody prepared against the starch granule-bound proteins effectively inhibited GBSSI activity, but had very little effect on the soluble starch synthases.173... 

Amylose is synthesized by granular-bound starch synthase, whereas amylopectin is synthesized by soluble starch synthase (Chapter 4).334,339 Because amylose is synthesized by the granular-bound starch synthase in a progressive manner,340 the amylose molecule is likely confined in the granule and has little opportunity to interact and form double helices with other starch molecules to facilitate branch formation. Branching reactions do occur on some amylose molecules, but at a much lower frequency than with amylopectin, and result in slightly branched amylose molecules. 

PROPERTIES OF THE SOLUBLE STARCH SYNTHASES FROM MAIZE ENDOSPERM... 

Rice Soluble Starch Synthase 372MPSRFEPCGLNQL 397GTGGLRDTV... 

It has been suggested that when plants are subjected to high temperature, starch synthase activity may be rate limiting. At temperatures higher than 30°C, both maize (Singletary et al., 1994) and wheat endosperm (Hawker and Jenner. 1993 Keeling et al, 1993, 1994 Jenner, 1994) had a reduction of starch deposition as compared with lower temperatures. In wheat, the starch biosynthetic enzyme affected was soluble starch synthase (SSS). 

Baba, T., Nishihara, M., Mizuno, K., Kawasaki, T., Shimada, H., Kobayashi, E., Ohnishi, S Tanaka, K., and Arai, Y. 1993. Identification, cDNA cloning and gene expression of soluble starch synthase in rice (Oryza sativa L.) immature seeds. Plant Physiol. 103, 565-573. 

Fontaine, T., D Hulst, C., Maddelein, M.-L., Routier, F., Pepin, T. M., Decq, A., Wieruszeski, J.-M., Delrue, B., Van Den Koornhuyse, N., Bossu, J.-P., Foumet, B., and Ball, S. 1993. Toward an understanding of the biogenesis of the starch granule Evidence that Chlamydo-monas soluble starch synthase II controls the synthesis of intermediate size glucans of amylopectin. J. BioL Chem. 268,16223-16230. 

Keeling, P. L., Bacon, P. J., and Holt, D. C. 1993. Elevated temperature reduces starch deposition in wheat endosperm by reducing the activity of soluble starch synthase. Planta 191, 342-348. 

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