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Articles

Nucleoside Diphosphate Sugar-Starch Glucosyl Transferase Activity of wx Starch Granules ¹

Department of Genetics, University of Wisconsin, Madison, Wisconsin

Starch granule preparations from the endosperm tissue of all waxy maize (Zea mays L.) mutants tested have low and approximately equal capability to incorporate glucose from adenosine diphosphate glucose into starch. As the substrate concentration is reduced, however, the activity of waxy preparations relative to nonmutant increases until, at the lowest substrate concentration utilized (0.1 µM), the activity of the waxy preparations is nearly equal to that of the nonmutant preparation. The apparent K_m (adenosine diphosphate glucose) for starch granule preparations from wx-C/wx-C/wx-C endosperms was 7.1 x 10^–5 M, which is compared to 3 x 10^–3 M for preparations from nonwaxy endosperms. Starch granule preparations from three other waxy mutants of independent mutational origin have levels of enzymic activity approximately equal to wx-C at a given substrate concentration giving rise to similar apparent K_m estimates. We conclude that there is in maize endosperm starch granules a second starch granule-bound glycosyl transferase, whose presence is revealed when mutation eliminates activity of the more active glucosyl transferase catalyzing the same reaction.

³ Present address: Department of Bacteriology, University of Wisconsin-Madison.

¹ Research was supported by the College of Agriculture and Life Sciences, University of Wisconsin-Madison and by National Institutes of Health Grant 15422. Paper No. 2229, Laboratory of Genetics.

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