Carbohydrate metabolism in the liver

Abstract

Several human glycogens have been analysed by enzymic methods and shown to have normal structures.The highly branched structure of rabbit liver glycogen has been verified by stepwise degradation using pullulanase and B-amylase. The actions of pullulanase on the B-amylase and glucamylase limit dextrins of glycogen were also investigated. Iodine complexes formed with rabbit liver glycogen are affected by low molecular weight aliphatic alcohols and by urea. The reaction of the former reagents is important in relation to the purification of glycogens by alcohol precipitation. Some attempt has been made to explain the reaction of urea on the basis of competitive hydrogen bonding."Extractable" glycogen was isolated from rat liver by extraction with dilute trichloracetic acid solution.The remaining "residual" glycogen was partially released by proteolytic digestion with Pronase, and isolated by gel filtration on a column of Sephadex G-75. The structures of these two glycogens were found to be similar. The ratio of "extractable" to "residual" glycogen was determined in fetal and adult rat and human liver tissues. The "residual" glycogen content of the developing liver appears to befairly constant but the "extractable" glycogen in the rat, at least, rises to a maximum at term and then falls.These results are discussed on the basis that "residual" glycogen is an artifact and that the level in the liver is governed by the molecular weight of the glycogen and the protein content. The development of the activities of glycogen synthetase (UDPG: 1 ,4-glucan a-4-glucosyltransferase ), phosphorylase (a-1 ,4-glucan: orthophosphate glucosyl-transferase), phosphoglucomutase (D-glucose-1,6-diphosphate: D-glucose-1-phosphate phosphotransferase) and glucose-6-phosphatase (D-glucose-6-phosphate phosphohydrolase) were examined in fetal and adult human livers, and the activities of these enzymes together with those of a-amylase (a-1,4-glucan 4-glucanohydrolase) and "acid maltase" (a-D-glucoside glucohydrolase) were also measured in fetal and neonatal rat livers. The results were analysed with reference to glycogen storage on the liver.Glycogen and enzyme analyses have been carried out on the tissues of four suspected cases of glycogen storage disease.