Lipid molecular order in liver mitochondrial outer membranes, and sensitivity of carnitine palmitoyltransferase I to malonyl‐CoA

Abstract

Mitochondrial outer membranes were prepared from livers of rats that were in the normal fed state, starved for 48 h, or made diabetic by injection of streptozotocin. Membranes were also prepared from starved late-pregnant rats. The latter three conditions have previously been shown to induce varying degrees of desensitization of mitochondrial overt carnitine palmitoyltransferase (CPT I) to malonyl-CoA inhibition. We measured the fluorescence polarization anisotropy of two probes, 1,6-diphenyl-1,3,5-hexatriene (DPH) and 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene-p-toluenes ulfonate (TMA-DPH) which, when incorporated into membranes, report on the hydrophobic core and on the peripheral regions of the bilayer, respectively. The corresponding polarization indices (rDPH and rTMA-DPH) were calculated. In membranes of all three conditions characterized by CPT I desensitization to malonyl-CoA, rDPH was decreased, whereas there was no change in rTMA-DPH, indicating that CPT I is sensitive to changes in membrane core, rather than peripheral, lipid order. The major lipid components of the membranes were analyzed. Although significant changes with physiological state were observed, there was no consistent pattern of changes in gross lipid composition accompanying the changes to membrane fluidity and CPT I sensitivity to malonyl-CoA. We conclude that CPT I kinetic characteristics are sensitive to changes in lipid composition that are localized to specific membrane microdomains.

Regulation of Carnitine Palmitoyltransferase (CPT) I during Fasting in Rainbow Trout (Oncorhynchus mykiss) Promotes Increased Mitochondrial Fatty Acid Oxidation

“…3). A similar response has been noted for mammalian liver-type CPT I iso- form (CPT Ia) in response to 24 h of fasting (Drynan et al 1996;Zammit et al 1998).…”

“…In mammals, mitochondrial membrane fluidity can be altered by a number of physiological states, including diabetes and starvation (Zammit et al 1997) and by ingesting a diet high in polyunsaturated fatty acids (Power et al 1994). In rat liver, starvation causes an increase in mitochondrial membrane fluidity (Zammit et al 1998) as well as a decrease in CPT I sensitivity to malonyl-CoA (Drynan et al 1996;Zammit et al 1998). In fish, membrane composition and fluidity are highly malleable by temperature (Hazel 1984) and diet (Guderley et al 2008;Morash et al 2008), but the effect of fasting is currently unclear.…”

The malonyl-CoA–long-chain acyl-CoA axis in the maintenance of mammalian cell function

“…It is to be emphasized that the sensitivity of L-CPTo to malonyl-CoA, as well as the K m for palmitoyl-CoA, are both modulated by physiological state [45][46][47][48] (but not in cardiac muscle [49]) and that these changes (i) can be mimicked by experimentally induced changes in the fluidity of the mitochondrial outer membrane in itro [50] and (ii) are correlated with changes in the molecular order of the lipids of outer membranes prepared from mitochondria isolated from livers of rats maintained under different physiological conditions [51]. It is inferred that protein-membrane interactions are likely to be important in determining the malonyl-CoA sensitivity of CPTo, and that they are likely to be due to interaction between the TM segments as well as between them and the annular membrane lipids [34].…”

“…Such interactions are also anticipated to modulate the degree of interaction between the N-and C-domains and may determine the kinetic characteristics of the protein under different physiological conditions. Therefore, it may be relevant that there are important structural differences between the predicted TM segments of the L-and M-isoforms of CPTo that may contribute towards their distinctive kinetic characteristics and their responses to membrane-fluidity changes in i o [51] and in itro [50,52].…”

“…In view of the dependence of CPTo activity on the physical state of the membrane [50,51], this may explain why ceramide appears to have a direct stimulatory effect on the activity of CPTo [138]. Such activation may, in turn, provide a feedback mechanism limiting the availability of acylCoA for further ceramide synthesis.…”