Labeling of Starch Granules by Bombardment with Tritium Atoms

Abstract

AbstractStarch granules were labeled by exposure to tritium atoms produced by thermal dissociation of tritium gas at a tungsten filament. Activity was shown by α‐amylase etching experiments to be confined to the surface of the granule. Dextrins and low molecular weight compounds could be partially resolved on Sephadex G‐75. The dextrin produced during tritiation had an elution volume corresponding to dextrin of 20–35 glucose units and was hydrolyzeable by α‐amylase. Labeled starch was hydrolyzed first with ß‐amylase and the limit dextrin hydrolyzed further with α‐amylase. A comparison of the specific activities of the maltoses produced by the two enzymes demonstrated that labeling was more heavily concentrated in outer brunches than in inner branches. Amylose obtained from labeled potato starch was purified by crystallization and on DEAE‐Sephadex columns. The ion‐exchange purified potato amylose was hydrolyzed with ß‐amylase with 50% of the activity retained in maltose. Tritium was found to be concentrated at the nonreducing ends of the amylose molecules. These results suggest that starch molecules are organized in granules with nonreducing ends oriented to the surface.