Enzyme-to-enzyme tunnelling between phosphoglucoisomerase and phosphofructokinase.
1. Cross-linked and permeabilized rat erythrocytes were incubated for 2-5 min at 37 degrees C in the presence of ATP and either D-[U-14C]glucose 6-phosphate (3 mM) mixed with unlabelled D-fructose 6-phosphate (1 mM) or D-[U-14C]fructose 6-phosphate (1 mM) mixed with unlabelled D-glucose 6-phosphate (3 mM). 2. The contribution of molecules derived from the radioactive ketohexose ester relative to the total amount of newly formed D-fructose 1,6-bisphosphate was lower than the time-related average value for such a relative contribution in the pool of D-fructose 6-phosphate. 3. From such a difference, it was calculated that, under the present experimental conditions, 13.1 +/- 2.0% of the molecules of D-fructose 1,6-bisphosphate formed during incubation are directly derived from D-glucose 6-phosphate by a process of enzyme-to-enzyme channelling between phosphoglucoisomerase and phosphofructokinase, rather than originating from the free pool of D-fructose 6-phosphate. 4. A comparable value of 13.2 +/- 3.2% was reached when the process of enzyme-to-enzyme tunnelling was judged from the 3H/14C ratio in D-fructose 1,6-bisphosphate formed by permeabilized erythrocytes exposed for 5-15 min to D-glucose 6-phosphate (3 or 5 mM) mixed with tracer amounts of both D-[1-14C]glucose 6-phosphate and D-[2-3H]glucose 6-phosphate.
Zähner
D
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Laboratory of Experimental Medicine, Erasmus Medical School, Brussels Free University, Belgium.
Malaisse
W J
WJ
D000818:Animals; D002250:Carbon Radioisotopes; D002463:Cell Membrane Permeability / Q000502:physiology; D004912:Erythrocytes / Q000201:enzymology*; D005636:Fructosephosphates / Q000097:blood*; D005956:Glucose-6-Phosphate Isomerase / Q000097:blood*; D010732:Phosphofructokinase-1 / Q000097:blood*; D051381:Rats
D002250:Carbon Radioisotopes; D005636:Fructosephosphates; C027618:fructose-6-phosphate; D010732:Phosphofructokinase-1; D005956:Glucose-6-Phosphate Isomerase