[Anomalous change in the specific conductivity in lipoproteins at around physiologic temperatures].
Studying the temperature dependence of conductivity sigma of rat and human lipoproteins and apoprotein A-I fractions revealed an anomalous region in the range of temperatures (35-38) +/- 0.5 degree C. The activation energy delta H and temperature coefficient sigma (delta sigma/delta T) on both sides of Tc and the heat of transition (delta H of transition) were calculated. In high-density human lipoproteins and apoA-I, the delta H value was found to be very low. Some mechanisms of interaction of hydrocortizone with high-density lipoproteins and apoA-I were studied by using IR-spectroscopy and conductometry were studied. It was found that the hormone considerably increases the portion of alpha-helices and beta-structures in these proteins (coil<-->alpha-helix and coil<-->beta-structure transitions). In this case, delta H value of the transition increases 13-fold; in addition, the abnormal region in apoA-I shifts 1-2 degrees C downwards. The anomalous changes in conductivity in the range of physiological temperatures in all lipoprotein fractions including apoA-I are probably related to structural phase transitions both in proteins and in phospholipids. Since the delta H value of the transition in human high-density lipoproteins is small, it is assumed that, in phospholipids of these particles, an orientation transition of the A<-->C smectic type takes place, which is assigned to the second-order phase transition. The structural transition in apoA-I can probably also be assigned to the second-order phase transition since the enthalpia of the transition is very small; presumably, this transition is related to changes in symmetry due to changes in the secondary structure (coil<-->beta-tructure transition).
Kunitsyn
V G
VG
Institute of Biochemistry, Russian Academy of Medical Sciences, Novosibirsk, Russia.
Panin
L E
LE
Poliakov
L M
LM
D000818:Animals; D016632:Apolipoprotein A-I / Q000737:chemistry*; D004553:Electric Conductivity; D006801:Humans; D006854:Hydrocortisone / Q000737:chemistry; D007700:Kinetics; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D013055:Spectrophotometry, Infrared; D013696:Temperature; D013816:Thermodynamics
D016632:Apolipoprotein A-I; D006854:Hydrocortisone