The stabilizing effect of albumin on structure-functional alteration of LH/
hCG receptors was analyzed by thermal perturbation technique. On exposing t
he membranes to bovine serum albumin (BSA) the heat inactivation profile of
hCG-binding sites was shifted to a temperature higher by about 5 degrees C
(T-50 values). The receptor destabilizing action of arachidonic and oleic
acids incorporated into ovarian membranes and reversal of this effect when
BSA was used as fatty acid scavenger, may indicate that free fatty acids ar
e responsible for the thermal instability of hCG-binding sites. This presum
ption was corroborated by digestion of membranes with phospholipase A(2) (P
LA(2)). This enzyme exerted effects on the thermal stability of the recepto
r protein resembling those observed upon insertion of fatty acids. The memb
rane fluidization induced by arachidonic acid can be reversed by BSA. Howev
er, alterations of lipid fluidity in membranes were not found to be a neces
sary prerequisite for stabilization of the LH/hCG receptor structure. Fluor
escence quenching studies indicated that incorporation of oleic acid or dig
estion of membrane phospholipids with PLA(2) elevated the accessibility of
fluorophores for acrylamide. BSA scavenging of free fatty acids approached
the quenching rate of control membranes. Analysis of fluorescence of membra
nes bound to monodansylcadaverine probe revealed that the negative surface
charge derived from free fatty acids resulted in destabilization of the rec
eptor protein. The effects of free fatty acids on membranes suggest that al
tered lipid-protein interactions may directly affect the stability of the L
H/hCG receptor structure. (C) 1999 Elsevier Science B.V. All rights reserve
d.