Calorimetric Determination of α-1, 4 Glucosidic Linkage Content in Starches and Glycogens

Abstract

1) Calorimetric studies on the enzymic hydrolyses of maltose, phenyl α-maltoside, isomaltose, maltotriose, panose and amylose have been made and the heats of hydrolysis of the α-1, 4 and α-1, 6 glucosidic linkages have been evaluated. 2) The heats of hydrolysis of α-l, 4 and α-1, 6 glucosidic linkages has been found to be approximately equal in their absolute magnitudes, but opposite in sign for the two linkages. It has also been found that the heat of hydrolysis of sugar compounds is obtainable as an ad ditive function of the thermal data of individual linkages to be hydrolyzed . 3) Calorimetric studies on the hydrolyses of starches and glycogens from various sources have been made and the α-1, 4 glucosidic linkage content in the respective sample has been determined by using the thermal data obtained for the two linkages. 4) Combining the data for linkage content with those concerning the amylose content of the starches determined by the amperometric titration method, the average length of unit chain of the amylopectin component has been evaluated. The average length of unit chain of the glycogens has also been evaluated. 5) The calorimetric method has been applied to the determination of the α-1, 4 gluco sidic linkage content in two kinds of sweet potato starch (i.e., Normn-1 and Okinawa-100) isolated at two different stages of development. It has been found that the sample isolated on October 31 (1953) had a higher value for α-1, 4 glucosidic linkage content than the sample isolated on August 6 (1953) for both the two sweet potato starches. The increase in α-1, 4 glucosidic linkage content has been found to be due to both the increases in amylose content and in average unit chain length of amylopectin component.