Effect of low frequency, low amplitude magnetic fields on the permeability of cationic liposomes entrapping carbonic anhydrase: II. No evidence for surface enzyme involvement.
Observations recently reported by our group indicate that combined 7 Hz sinusoidal (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 across carbonic anhydrase (CA)-loaded liposomes (DPPC:Chol:SA). A direct involvement of charges of stearylamine (SA) on the lipid membrane surface was also demonstrated. Kinetic studies showed that CA was mainly entrapped in liposomes at 5:3:2 molar ratio, although a small amount (17%) of enzyme was also located on the external surface of these cationic liposomes. In this paper 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 samples was observed. On the contrary the apparent V(max) was increased by approximately a factor of 2 after field exposure. In spite of the proteolytic digestion of this external CA, a significant increase of enzymatic activity, as a function of increase in the diffusion rate of substrate across the lipid bilayer, was observed in the exposed samples. Based on these results, a conformational 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 developed.
Ramundo-Orlando
A
A
Institute of Experimental Medicine, CNR, Rome, Italy.
Mattia
F
F
Palombo
A
A
D'Inzeo
G
G
D000818:Animals; D001698:Biomedical Engineering; D019149:Bioreactors; D002256:Carbonic Anhydrases / Q000737:chemistry / Q000378:metabolism; D002412:Cations; D002417:Cattle; D004574:Electromagnetic Fields / Q000009:adverse effects*; D066298:In Vitro Techniques; D007700:Kinetics; D008081:Liposomes; D010539:Permeability; D011487:Protein Conformation
D002412:Cations; D008081:Liposomes; D002256:Carbonic Anhydrases