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S. R. Erlander. Copyright 1960 by the American Association of Cereal Chemists, Inc. Experimental evidence indicates that amylose and amylopectin are produced simultaneously. Consequently, any proposed mechanism for the synthesis of starch based on the assumption that the branching enzyme is inactivated at some time during the day, in order to enable the synthesis of amylose, would appear to be invalid. Amylose (3.1%) was produced in very immature waxy corn endosperm by covering the ears with cellophane bags. One can postulate that the production of starch by plants occurs via glycogen. That is, plant glycogen is attacked by a theoretical debranching enzyme which (a) removed the outer or available branches of the glycogen to form amylopectin and then (b) connects these removed branches end-to-end to form amylose. In normal waxy endosperm the absence of amylose can be explained by assuming the presence of an inhibitor of the proposed debranching enzyme. The production of amylose in very immature waxy corn endosperm indicates that the activity of this inhibitor may be diminished by retarding the growth of certain factors in the very immature waxy corn endosperm. The average chain length of amylose appears to increase with an increase in the average chain length of the corresponding amylopectin. These results can be explained by assuming that the degree of polymerization of the unit chains removed by the proposed debranching enzyme remains constant. Consequently, the degree of polymerization of an amylose appears to be a function of the chain length of its parent glycogen. |
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