THYROID-HORMONES ALTER ARRHENIUS KINETICS OF SUCCINATE-2,6-DICHLOROINDOPHENOL REDUCTASE, AND THE LIPID-COMPOSITION AND MEMBRANE FLUIDITY OFRAT-LIVER MITOCHONDRIA
Dv. Parmar et al., THYROID-HORMONES ALTER ARRHENIUS KINETICS OF SUCCINATE-2,6-DICHLOROINDOPHENOL REDUCTASE, AND THE LIPID-COMPOSITION AND MEMBRANE FLUIDITY OFRAT-LIVER MITOCHONDRIA, European journal of biochemistry, 230(2), 1995, pp. 576-581
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-dichloro
indophenol reductase (SDR) and membrane fluidity. Thyroidectomy caused
substantial decrease in the total phospholipid and cholesterol conten
ts; the proportion of all phospholipid components was also decreased s
ignificantly (50-100% decrease). The energy of activation, E(1), for S
DR decreased with a concomitant increase in the membrane fluidity. Tre
atment with physiologic doses or replacement doses of L-thyroxine resu
lted 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 E(1) and E(2). Tr
eatment with L-thyroxine restored membrane fluidity to almost euthyroi
d values, Regression analysis suggested a role for phosphatidylcholine
, phosphatidylethanolanline, phosphatidylserine and phosphatidylinosit
ol microdomains in modulating the SDR activity. Membrane fluidity was
strongly correlated with total phospholipid, cholesterol, diphosphatid
ylglycerol and phosphatidyl-inositol, and the ratio of cholesterol/tot
al phospholipid (mol/mol).