Enzyme-to-enzyme tunnelling between phosphoglucoisomerase and phosphofructokinase

Abstract

1. 1. Cross-linked and permeabilized rat erythrocytes were incubated for 2–5 min at 37 °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. 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 averaged value for such a relative contribution in the pool of D-fructose 6-phosphate. 3. 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. 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 o-glucoe 6-phosphate (3 or 5mM) mixed with tracer amounts of both D-[l-'4C]glucose 6-phosphate and D-[2- −3 2+H]glucose 6-phosphate.