The interrelationship between glycogen structure and metabolism
Abstract (Summary)Restricted Item. Print thesis available in the University of Auckland Library or available through Inter-Library Loan. The development of a new, easy and affordable method of fractionation, which allows the separation of the high molecular weight from the low molecular weight glycogen was achieved. This method using 1.09 M sodium citrate as the separating medium was developed to facilitate research on muscle samples which are difficult to manipulate and also produce a relatively low yield of glycogen. Dynamic-laser-light-scattering (DLS) was used to determine the average radius of glycogen samples within the different solvents used within this thesis. Aggregative properties of each solvent were ascertained from these results. DLS indicated that sucrose had minor aggregative properties over the entire molecular weight range, but sodium citrate possessed aggregative properties over only the high molecular weight glycogen. Experiments using the reducing agent ?-mercaptoethanol, and the acetylating agent iodoacetamide, under a non-oxygen atmosphere, reproduced results from previous experiments. These experiments indicated the presence of a glycogen protein backbone that possessed disulphide bonds as an essential component of the high molecular weight glycogen. Subsequent enzymic analysis together with further reductions indicated the presence of hidden cysteine residues that can potentially form disulphide bonds. Nuclear magnetic resonance (NMR) was developed as a new and powerful technique for the investigation of glycogen. Research using this technique concurred with all of the conclusions from the previous reduction/enzymic degradations. Conditions of starvation and refeeding were altered to determine the differing effect on muscle and liver. Both organs were shown to go through progressive starvation followed by overproduction of glycogen once feeding was reinitiated, but these were at different rates. Under conditions that produce less than a 50% depletion of muscle glycogen, radioisotope labelling of de novo glycogen indicated that the lysosomal (high molecular weight) store employs a feedback mechanism that stops any further production of this store of glycogen. These results indicate the differences and importance of separating the lysosomal store from the cytosolic store of glycogen. Overall the results indicate the important interrelationship between glycogen structure and its metabolism. Glycogen is a proteoglycan of vast polydispersity, which depending on its structure, will associate with the cytosolic and/or lysosomal compartments of cells. Even the widely accepted Cori Cycle cannot explain the tissue and subcellular interactions of glycogen, glucose and lactate.
School Location:New Zealand
Source Type:Master's Thesis
Date of Publication:01/01/1993