Starch synthase activity

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... 

It is widely accepted that GBSS activity is a function of the protein coded by the waxy gene. The waxy locus gene product is a protein of molecular weight 58 KDa that is associated with starch granules and is similar to that found for the solubilized maize endosperm GBSSI.173 This protein has been extracted by heating the starch with a solution of SDS or by incubation at 37°C with 9M urea, but starch synthase activity... 

Since then, starch synthase activity has been reported to be present in many plant extracts (for reviews, see Preiss and Levi, 1980 Preiss and Sivak, 1996). 

Attempts to elute or solubilize the activity had met with little success until Macdonald and Preiss (1983, 1985) incubated ground maize starch granules with a-amylase and glucoamylase. The solubilized starch synthase activity was chromatographed on an anion exchange column and two peaks of activity were obtained, with 80% of the activity residing with starch synthase I, which eluted from the DEAE-cellulose column at a lower salt concentration than the starch synthase II fraction. 

Shure et al. (1983) prepared cDNA clones homologous to Wx mRNA. In subsequent experiments (Federoff et al., 1983), restriction endonuclease fragments containing part of the Wx locus were cloned from strains carrying the ac wx-M9, wa-M9, and wx-M6 alleles to characterize further the controlling insertion elements activator (ac) and dissociation (ds). Excision of the ds element from the certain wx alleles produces two new alleles (S5 and S9) that are encoding the wx proteins having altered starch synthase activities (Wessler et al., 1986). Two of these, S9 and S5, had 53 and 32% of the starch synthase activity, respectively, seen in the normal endosperm. Mutant... 

S9, with higher starch synthase activity, had 36% of the amylose content observed in the nonmutant endosperm, whereas mutant S5, with an even lower starch synthase activity of 32%, had only 21% of the nonmutant maize amylose content. These data further support the view that the waxy protein is involved in amylose synthesis. 

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). 

Delrue, B., Fontaine, T., Routier, F., Decq. A., Wieruszeski, J.-M., Van Den Koomhuyse, N., Maddelein, M.-L., Fournet, B., and Ball, S. 1992. Waxy Chlamydomonas reinhardtii Monocellular algal mutants defective in amylose synthesis and granule-bound starch synthase activity accumulate a structurally modified amylopectin. J. BacterioL 174,3612-3620. 

Chlamydomonas reinhardtii monocellular algal mutants defective in amylose biosynthesis and granule-bound starch synthase activity accumulate a structurally modified amylopectin. J. Bac-teriol. 1992 174 3612-3620. 

Measurement of Starch Synthase Activity in Starch Granules. 1467... 

Measurement of Soluble Starch Synthase Activity in a Plant Extract. 1468... 

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