INTERPRETATION OF THE EFFECT OF AN OSCILLATING ELECTRIC-FIELD ON MEMBRANE ENZYMES

Theoretical expressions for the frequency and amplitude dependence of the rate of a catalyzed reaction are fitted to the data of Graziana et al. (1990) [Graziana, A., Ranjeva, R., & Teissie, J. (1990) Biochemistry 29, 8313-83181 for Ca2+ uptake by carrot protoplasts in an oscillating electric field. This uptake is a direct (linear) measure of the rate of increase of ATP caused by a plasma membrane enzyme in the oscillating field. The fit gives 20 ms and 33-mu-s for the relaxation times of the enzyme and roughly 3 for the effective number of elementary changes displaced across the membrane by a conformational change of the enzyme in its catalytic cycle. Additional experiments are suggested to define further the mechanism of the enzymatic reaction.