Thyroid hormones alter Arrhenius kinetics of succinate-2,6-dichloroindophenol reductase, and the lipid composition and membrane fluidity of rat liver mitochondria.
Thyroid-status-dependent changes in lipid/phospholipid profiles in rat liver mitochondria were examined and attempts were made to correlate the observed changes with kinetic parameters of succinate-2,6-dichloroindophenol reductase (SDR) and membrane fluidity. Thyroidectomy caused substantial decrease in the total phospholipid and cholesterol contents; the proportion of all phospholipid components was also decreased significantly (50-100% decrease). The energy of activation, E1, for SDR decreased with a concomitant increase in the membrane fluidity. Treatment with physiologic doses or replacement doses of L-thyroxine resulted in partial restoration of lipid/phospholipid components. However, the SDR activity decreased with a simultaneous elevation in the phase-transition temperature and significant decreases in E1 and E2. Treatment with L-thyroxine restored membrane fluidity to almost euthyroid values. Regression analysis suggested a role for phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine and phosphatidylinositol microdomains in modulating the SDR activity. Membrane fluidity was strongly correlated with total phospholipid, cholesterol, diphosphatidylglycerol and phosphatidyl-inositol, and the ratio of cholesterol/total phospholipid (mol/mol).
Parmar
D V
DV
Department of Biochemistry, Faculty of Science, M. S. University of Baroda, India.
Khandkar
M A
MA
Pereira
L
L
Bangur
C S
CS
Katyare
S S
SS
D000818:Animals; D002784:Cholesterol / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D008560:Membrane Fluidity / Q000502:physiology*; D008930:Mitochondria, Liver / Q000201:enzymology* / Q000378:metabolism / Q000648:ultrastructure; D010088:Oxidoreductases / Q000378:metabolism*; D010743:Phospholipids / Q000378:metabolism*; D051381:Rats; D013696:Temperature; D013963:Thyroid Hormones / Q000502:physiology*
D010743:Phospholipids; D013963:Thyroid Hormones; D002784:Cholesterol; D010088:Oxidoreductases; C022690:succinic-dichloroindophenol reductase