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R Geddes

Publications and source records attributed to R Geddes.

45 records · Page 3Linked to original sources
PubMed1977

The molecular size and shape of liver glycogen.

The molecular-weight distribution of liver glycogen has been established from the analysis of sedimentation rates of fractions separated on sucrose density gradients and from the direct measurement of the diffusion coefficients of these fractions by laser-intensity-fluctuation spectroscopy. Hydrodynamic studies indicated that all fractions of glycogen of mol.wt.exceeding 25x10(6) had about 1.1 g of water per g of polysaccharide associated with them. The hydration and hydrodynamic behaviour of all fractions of mol.wt. exceeding 25x10(6) was similar, whereas smaller fractions behaved anomalously, indicating a substantially different overall structure.

Centrifugation, Density Gradient↗
PubMed1977

Molecular and metabolic heterogeneity of liver glycogen.

On refeeding after starvation, the resynthesis of rabbit-liver glycogen proceeds inhomogeneously and over-produces material of low molecular weight. The fate of radioactivity incorporated into glycogen from D-glucose-14C can be explained if glycogen of high molecular weight is synthesised on a protein backbone. Confirmation of this view is given by the effect upon glycogen of reagents that break disulphide bonds; these cause loss of the polysaccharide of high molecular weight. Buoyant densities of glycogens are found to be independent of molecular weight and even of extensive degradation. It is concluded that glycogen synthesis proceeds by two routes; one results in the production of polysaccharide of high molecular weight which has a protein backbone capable of forming disulphide bonds, and another results in the production of polysaccharide of low molecular weight which has either no protein backbone or a protein backbone that is incapable of forming disulphide bridges. Apart from size, the two species are physicochemically indistinguishable.

Animals↗
PubMed1977

Hydrodynamic properties of 2-mercaptoethanol-modified glycogen.

Treatment of glycogen with 2-mercaptoethanol and iodoacetamide gives rise to a modified glycogen which resembles the original glycogen in its hydrodynamic behaviour but has a pronounced tendency to aggregate. The modified glycogen can be distinguished easily, by its diffusion coefficient, from glycogen degraded by more traditional methods of extraction. The 'fundamental' glycogen particle appears to be composed of two or three glycogen beta-particles linked by a single protein chain.

Animals↗
PubMedDate not supplied

The structure of placental glycogen.

Glycogen was purified from human term placenta and its structural features investigated. The beta-amylolysis limit and average chain lengths indicated that some degradation of the glycogen had occurred prior to its extraction. The sedimentation coefficient distribution of the purified glycogen showed that it contained a significant proportion of aggregated material. Diffusion coefficient measurements allowed calculation of the molecular weight distribution. The placental glycogen contained a significant proportion of high molecular weight material, although not as much as liver or skeletal muscle glycogens. Because the high molecular weight glycogen of liver and skeletal muscle is associated with the lysosome it is likely that this is also true of the large placental glycogen. Lysosomal glycogen is degraded hydrolytically to glucose and so placental glycogen may be involved in fetal glucose homeostasis.

Chemical Phenomena↗
PubMedDate not supplied

Glycogen metabolism in the rat visceral yolk sac. I. Glycogen content and gestational age.

The glycogen content of the rat visceral yolk sac was determined between 13.5 and 20.5 days of gestation by the best available colorimetric method. The concentration of glycogen in the tissue increased ten-fold between 13.5 and 18.5 days, to reach a value similar to that for mammalian muscle, but then decreased by 50 per cent between 18.5 and 20.5 days. Determination of the iodine-iodide spectra and fractionation of the glycogen particles by a novel sodium citrate centrifugation method indicated broad similarities between the structures of glycogen particles, isolated by a mild phenol-water method, from the yolk sac and the liver of the rat. However, the proportion of 'high'-molecular-weight glycogen in the yolk sac increases between 18.5 and 20.5 days, as a result of the preferential loss of 'low'-molecular-weight glycogen, so that at term the proportion approaches that found in liver glycogen.

Animals↗