MAGNESIUM STRENGTHENS LIPID PACKING IN PROTEOLIPOSOMES-CONTAINING MITOCHONDRIAL H~+-ATPase
Mg~(2+)加强嵌有H~+-ATP酶脂酶体脂质分子的堆积(packing)

Merocyanine MC 540(MC 540) , a lipohilic and sensitive probe to changes of dynamic charateristic in membrane lipids, can be used to study lipid packing in bilayer by measuring the enhancement of fluorescence intensity of the dye which results when the dye enters the hydrophobic environment of the membranes. Higher the fluorescence intensity, looser the degree of lipid packing, and viseversa.In this paper, the fluorescence responses of binding of MC 540 to the proteoliposomes-containing mitochondrial H+-ATPase in the absence and presence of Mg2+(l mM). were compared. The results clearlz show that the fluorescence intensity for the former was 30% higher than that for the later. This would mean that lipid molecules in the bilayer are closely spaced and become more ordering which results in tightness of degree of the lipid packing for the proteoliposomes in the presenc of Mg2+ compared with that in the absence of Mg2+ . And other hand, the results on energy transfer between n-(9-anthroyl-oxy)fatty acid probes (n = 2,7, and 16) and bound MC 540 in the vesicles indicate that the efficiencies of energy transfer between 2-AP and MC 540 was highest for the proteoliposomes in the presence of Mg2+ compared with that in the absence of Mg2+. It may indicate that the change of the lipid packing detected by MC 540 probe is mainly located in the lipid packing near the bilayer surface. Proper fluidity in the proteolposomes-containing Mg2+ is modulated by Mg2+ inducing formation of the proper degree of the lipid packing near the bilayer surface which would favour the forming of a suitable conformation of the H + -ATPase with higher activities. Therefore, the results described here, more direct evidence for the hypothetic model on the role of Mg2+ in the reconstitution of mitochondrial H+ -ATPase on liposomes has further been presented.