Interconversion of D-fructose 1,6-bisphosphate and triose phosphates in human erythrocytes.
Aldolase and triose phosphate isomerase both display strict specificity towards the enantiomers of [1-3H]glycerone 3-phosphate. The enantiomer generated from D-[1-3H]glyceraldehyde 3-phosphate produces 3HOH in the aldolase reaction, whilst the other enantiomer generated from D-[3-3H]fructose 1,6-bisphosphate is solely detritiated in the reaction catalyzed by triose phosphate isomerase. Advantage was taken of such a specificity to assess, in human erythrocytes exposed to either D-[3-3H]glucose or D-[3,4-3H]glucose, the extent of D-glyceraldehyde 3-phosphate sequential conversion to glycerone 3-phosphate and D-fructose 1,6-bisphosphate, relative to net glycolytic flux. At 37 degrees C and in the presence of 5.6 mM D-glucose, only 55% of the metabolites of D-[4-3H]glucose underwent detritiation in the reactions catalyzed by triose phosphate isomerase and aldolase. Such a percentage was further decreased at low temperature (8 degrees C) or lower concentrations of D-glucose (0.2 and 1.0 mM). However, when the erythrocytes were exposed to menadione, the increase in 3HOH production from either D-[3-3H]glucose or D-[3,4-3H]glucose indicated that the majority of the 3H atoms initially located on the C4 of D-glucose were recovered as 3HOH upon circulation through the pentose phosphate pathway. These findings suggest that, under physiological conditions, a large fraction of D-glyceraldehyde 3-phosphate generated from exogenous D-glucose may undergo enzyme-to-enzyme channelling in the glycolytic pathway.
Maggetto
C
C
Laboratory of Experimental Medicine, Brussels Free University, Belgium.
Manuel y Keenoy
B
B
Zähner
D
D
Bodur
H
H
Sener
A
A
Malaisse
W J
WJ
D001786:Blood Glucose / Q000378:metabolism; D004912:Erythrocytes / Q000378:metabolism*; D005634:Fructose-Bisphosphate Aldolase / Q000097:blood; D005635:Fructosediphosphates / Q000097:blood*; D005986:Glyceraldehyde 3-Phosphate / Q000097:blood*; D005994:Glycerophosphates / Q000097:blood*; D006801:Humans; D007536:Isomerism; D007700:Kinetics; D011865:Radioisotope Dilution Technique; D014305:Triose-Phosphate Isomerase / Q000097:blood; D014316:Tritium
D001786:Blood Glucose; D005635:Fructosediphosphates; D005994:Glycerophosphates; D014316:Tritium; D005986:Glyceraldehyde 3-Phosphate; C029620:alpha-glycerophosphoric acid; D005634:Fructose-Bisphosphate Aldolase; D014305:Triose-Phosphate Isomerase; C029063:fructose-1,6-diphosphate