Effect of low frequency, low amplitude magnetic fields on the permeabilityof cationic liposomes entrapping carbonic anhydrase II. No evidence for surface enzyme involvement
A. Ramundo-orlando et al., Effect of low frequency, low amplitude magnetic fields on the permeabilityof cationic liposomes entrapping carbonic anhydrase II. No evidence for surface enzyme involvement, BIOELECTROM, 21(7), 2000, pp. 499-507
Observations recently reported by our group indicate that combined 7 Hz sin
usoidal (B-acpeak = 50 mu T) and parallel static (B-dc = 50 mu T) magnetic
fields can induce a significant increase in diffusion rate of substrate acr
oss carbonic anhydrase (CA)-loaded liposomes (DPPC:Chol:SA). A direct invol
vement of charges of stearylamine (SA) on the lipid membrane surface was al
so demonstrated. Kinetic studies showed that CA. was mainly entrapped in Li
posomes at 5:3:2 molar ratio, although a small amount (17%) of enzyme was a
lso located on the external surface of these cationic liposomes. In this pa
per we report steady state kinetic studies on this latter CA after ELF-EMFs
exposure. No difference in the apparent K-m between exposed and sham sampl
es was observed. On the contrary the apparent V-max was increased by approx
imately a factor of 2 after field exposure. In spite of the proteolytic dig
estion of this external CA, a significant increase of enzymatic activity, a
s a function of increase in the diffusion rate of substrate across the lipi
d bilayer, was observed in the exposed samples. Based on these results, a c
onformational change induced by the field on the CA located on the external
surface of 5:3:2 liposomes is excluded as an explanation for our previous
observations, supporting the primary role of bilayer SA in the interaction
with ELF A model of ELF interaction, based on the Larmor precession theory,
explaining the physical phenomenon induced on the dipole of SA has been de
veloped. (C) 2000 Wiley-Liss, Inc.