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Plant Physiol. Dec 1979; 64(6): 1039–1042.
PMCID: PMC543187

Properties of Citrate-stimulated Starch Synthesis Catalyzed by Starch Synthase I of Developing Maize Kernels 1


Chromatography of extracts of maize on diethylaminoethyl-cellulose resolves starch synthase activity into two fractions (Ozbun, Hawker, Preiss 1971 Plant Physiol 48: 785-769). Only starch synthase I is capable of synthesis in the absence of added primer and the presence of 0.5 molar citrate. This enzyme fraction has been purified about 1,000-fold from maize kernels homozygous for the endosperm mutant amylose-extender (ae). Because ae endosperm lacks the starch-branching enzyme which normally purifies with starch synthase I, the final enzyme fraction was free of detectable branching enzyme activity. This allowed a detailed characterization of the citrate-stimulated reaction. The citrate-stimulated reaction was dependent upon citrate concentrations of greater than 0.1 molar. However, the reaction is not specific for citrate and malate also stimulated the reaction. Branching enzyme increased the velocity of the reaction about 4-fold but did not replace the requirement for citrate. Citrate reduced the Km for the primers amylopectin and glycogen from 122 and 595 micrograms per milliliter, respectively, to 6 and 50 micrograms per milliliter, respectively. The enzyme was found to contain 1.7 milligrams of anhydroglucose units per enzyme unit. Thus reaction mixtures contained 1 to 5 micrograms (5 to 25 micrograms per milliliter) of endogenous primer. The citrate-stimulated reaction could be explained by an increased affinity for this endogenous primer. The starch synthase reaction in the absence of primer is dependent upon several factors including endogenous primer concentration, citrate concentration as well as branching enzyme concentration.

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Selected References

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  • Ozbun JL, Hawker JS, Preiss J. Adenosine diphosphoglucose-starch glucosyltransferases from developing kernels of waxy maize. Plant Physiol. 1971 Dec;48(6):765–769. [PMC free article] [PubMed]
  • Boyer CD, Preiss J. Multiple forms of starch branching enzyme of maize: evidence for independent genetic control. Biochem Biophys Res Commun. 1978 Jan 13;80(1):169–175. [PubMed]
  • Fox J, Kawaguchi K, Greenberg E, Preiss J. Biosynthesis of bacterial glycogen. Purification and properties of the Escherichia coli B ADPglucose:1,4-alpha-D-glucan 4-alpha-glucosyltransferase. Biochemistry. 1976 Feb 24;15(4):849–857. [PubMed]
  • Ghosh HP, Preiss J. Biosynthesis of starch in spinach chloroplasts. Biochemistry. 1965 Jul;4(7):1354–1361. [PubMed]
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  • Kawaguchi K, Fox J, Holmes E, Boyer C, Preiss J. De novo synthesis of Escherichia coli glycogen is due to primer associated with glycogen synthase and activation by branching enzyme. Arch Biochem Biophys. 1978 Oct;190(2):385–397. [PubMed]
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  • Ozbun JL, Hawker JS, Preiss J. Adenosine diphosphoglucose-starch glucosyltransferases from developing kernels of waxy maize. Plant Physiol. 1971 Dec;48(6):765–769. [PMC free article] [PubMed]
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Articles from Plant Physiology are provided here courtesy of American Society of Plant Biologists


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