Anomeric specificity of D-[U-14C]glucose incorporation into glycogen in rat hemidiaphragms.
The anomeric specificity of D-[U-14C]glucose incorporation into glycogen in rat hemidiaphragms was investigated. For this purpose, the hemidiaphragms were preincubated for 30 min at 37 degrees C and then incubated for 5 min at the same temperature in the presence of alpha- or beta-D-[U-14C]glucose. The concentrations of D-glucose (5.6 or 8.8 mM) and insulin (0 or 10 mU/ml) were identical during the preincubation and incubation periods. The incubation medium was prepared in D2O/H2O (3:1, v/v) in order to delay the interconversion of the D-glucose anomers. In addition to glycogen labelling, the output of radioactive acidic metabolites was also measured. Insulin caused a preferential stimulation of glycogen labelling relative to glycolysis. Such was not the case in response to a rise in D-glucose concentration. At 5.6 mM D-glucose and whether in the presence or absence of insulin, both glycogen labelling and glycolysis were lower with alpha-D-glucose than with beta-D-glucose suggesting a higher rate of beta-D-glucose than alpha-D-glucose transport across the plasma membrane. A mirror image was found at 8.8 mM D-glucose, especially in the absence of insulin. At this close-to-physiological hexose concentration, insulin lowered the alpha/beta ratio for glycogen labelling. On the contrary, the rise in D-glucose concentration increased such a ratio. Since such a rise is probably little affected by any possible anomeric difference in D-glucose transport across the plasma membrane, the present results strongly suggest that the intracellular factors regulating net glycogen synthesis, as well as glycolytic flux, display obvious preference for alpha-D-glucose.
Zhang
Ying
Y
Laboratory of Experimental Hormonology, Erasmus Medical School, Brussels Free University, 808 Route de Lennik, B-1070 Brussels, Belgium.
Courtois
Philippe
P
Sener
Abdullah
A
Malaisse
Willy J
WJ
D000818:Animals; D002250:Carbon Radioisotopes / Q000378:metabolism; D003903:Deuterium / Q000378:metabolism; D003964:Diaphragm / Q000378:metabolism*; D005260:Female; D005947:Glucose / Q000737:chemistry* / Q000378:metabolism*; D006003:Glycogen / Q000378:metabolism*; D006019:Glycolysis; D019344:Lactic Acid / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D013237:Stereoisomerism; D013379:Substrate Specificity
D002250:Carbon Radioisotopes; D019344:Lactic Acid; D006003:Glycogen; D003903:Deuterium; D005947:Glucose