The Evaluation of the Effects of Dietary Vitamin E or Selenium on Lipid Oxidation in Rabbit Hamburgers: Comparing TBARS and Hexanal SPME-GC Analyses.

The effects and specificity of dietary supplementation of EconomasETM (EcoE), mainly consisting of organic selenium (0.15 or 0.30 mg/kg feed; Se) or of vitamin E (100 or 200 mg/kg feed; VE), on lipid oxidation were evaluated in rabbit hamburgers during refrigerated storage. Oxidation data obtained by thiobarbituric acid-reactive substances (TBARS) spectrophotometric analysis and solid-phase microextraction (SPME) coupled with gas chromatography (GC) to determine hexanal content were compared. The relationships between oxidation levels, colour and pH and the discriminability of EcoE- or VE-treatment compared with control were also examined. TBARS content decreased in both VE and EcoE groups, while hexanal showed lower values only in the VE100 dietary group. The colour parameters were compatible with acceptable product quality and seemed to parallel the TBARS values up to the second day storage. Both VE and EcoE improved oxidative stability without affecting the sensory properties, but the VE effect appeared to more specifically hamper lipid oxidation, as evidenced by the determination and quantification of hexanal, a specific product of fatty acid peroxidation.

The mitochondrial F1FO-ATPase exploits the dithiol redox state to modulate the permeability transition pore.

The dithiol reagents phenylarsine oxide (PAO) and dibromobimane (DBrB) have opposite effects on the F1FO-ATPase activity. PAO 20% increases ATP hydrolysis at 50 µM when the enzyme activity is activated by the natural cofactor Mg2+ and at 150 µM when it is activated by Ca2+. The PAO-driven F1FO-ATPase activation is reverted to the basal activity by 50 µM dithiothreitol (DTE). Conversely, 300 µM DBrB decreases the F1FO-ATPase activity by 25% when activated by Mg2+ and by 50% when activated by Ca2+. In both cases, the F1FO-ATPase inhibition by DBrB is insensitive to DTE. The mitochondrial permeability transition pore (mPTP) formation, related to the Ca2+-dependent F1FO-ATPase activity, is stimulated by PAO and desensitized by DBrB. Since PAO and DBrB apparently form adducts with different cysteine couples, the results highlight the crucial role of cross-linking of vicinal dithiols on the F1FO-ATPase, with (ir)reversible redox states, in the mPTP modulation.

Molecular and Supramolecular Structure of the Mitochondrial Oxidative Phosphorylation System: Implications for Pathology.

Under aerobic conditions, mitochondrial oxidative phosphorylation (OXPHOS) converts the energy released by nutrient oxidation into ATP, the currency of living organisms. The whole biochemical machinery is hosted by the inner mitochondrial membrane (mtIM) where the protonmotive force built by respiratory complexes, dynamically assembled as super-complexes, allows the F1FO-ATP synthase to make ATP from ADP + Pi. Recently mitochondria emerged not only as cell powerhouses, but also as signaling hubs by way of reactive oxygen species (ROS) production. However, when ROS removal systems and/or OXPHOS constituents are defective, the physiological ROS generation can cause ROS imbalance and oxidative stress, which in turn damages cell components. Moreover, the morphology of mitochondria rules cell fate and the formation of the mitochondrial permeability transition pore in the mtIM, which, most likely with the F1FO-ATP synthase contribution, permeabilizes mitochondria and leads to cell death. As the multiple mitochondrial functions are mutually interconnected, changes in protein composition by mutations or in supercomplex assembly and/or in membrane structures often generate a dysfunctional cascade and lead to life-incompatible diseases or severe syndromes. The known structural/functional changes in mitochondrial proteins and structures, which impact mitochondrial bioenergetics because of an impaired or defective energy transduction system, here reviewed, constitute the main biochemical damage in a variety of genetic and age-related diseases.

Sulfide affects the mitochondrial respiration, the Ca2+-activated F1FO-ATPase activity and the permeability transition pore but does not change the Mg2+-activated F1FO-ATPase activity in swine heart mitochondria.

In mammalian cells enzymatic and non-enzymatic pathways produce H2S, a gaseous transmitter which recently emerged as promising therapeutic agent and modulator of mitochondrial bioenergetics. To explore this topic, the H2S donor NaHS, at micromolar concentrations, was tested on swine heart mitochondria. NaHS did not affect the F1FO-ATPase activated by the natural cofactor Mg2, but, when Mg2+ was replaced by Ca2+, a slight 15% enzyme inhibition at 100 µM NaHS was shown. Conversely, both the NADH-O2 and succinate-O2 oxidoreductase activities were totally inhibited by 200 µM NaHS with IC50 values of 61.6 ± 4.1 and 16.5 ± 4.6 µM NaHS, respectively. Since the mitochondrial respiration was equally inhibited by NaHS at both first or second respiratory substrates sites, the H2S generation may prevent the electron transfer from complexes I and II to downhill respiratory chain complexes, probably because H2S competes with O2 in complex IV, thus reducing membrane potential as a consequence of the cytochrome c oxidase activity inhibition. The Complex IV blockage by H2S was consistent with the linear concentration-dependent NADH-O2 oxidoreductase inhibition and exponential succinate-O2 oxidoreductase inhibition by NaHS, whereas the coupling between substrate oxidation and phosphorylation was unaffected by NaHS. Even if H2S is known to cause sulfhydration of cysteine residues, thiol oxidizing (GSSG) or reducing (DTE) agents, did not affect the F1FO-ATPase activities and mitochondrial respiration, thus ruling out any involvement of post-translational modifications of thiols. The permeability transition pore, the lethal channel which forms when the F1FO-ATPase is stimulated by Ca2+, did not open in the presence of NaHS, which showed a similar effect to ruthenium red, thus suggesting a putative Ca2+ transport cycle inhibition.

Mitochondrial F1FO-ATPase and permeability transition pore response to sulfide in the midgut gland of Mytilus galloprovincialis.

The molecular mechanisms which rule the formation and opening of the mitochondrial permeability transition pore (mPTP), the lethal mechanism which permeabilizes mitochondria to water and solutes and drives the cell to death, are still unclear and particularly little investigated in invertebrates. Since Ca2+ increase in mitochondria is accompanied by mPTP opening and the participation of the mitochondrial F1FO-ATPase in the mPTP is increasingly sustained, the substitution of the natural cofactor Mg2+ by Ca2+ in the F1FO-ATPase activation has been involved in the mPTP mechanism. In mussel midgut gland mitochondria the similar kinetic properties of the Mg2+- or Ca2+-dependent F1FO-ATPase activities, namely the same affinity for ATP and bi-site activation kinetics by the ATP substrate, in spite of the higher enzyme activity and coupling efficiency of the Mg2+-dependent F1FO-ATPase, suggest that both enzyme activities are involved in the bioenergetic machinery. Other than being a mitochondrial poison and environmental contaminant, sulfide at low concentrations acts as gaseous mediator and can induce post-translational modifications of proteins. The sulfide donor NaHS, at micromolar concentrations, does not alter the two F1FO-ATPase activities, but desensitizes the mPTP to Ca2+ input. Unexpectedly, NaHS, under the conditions tested, points out a chemical refractoriness of both F1FO-ATPase activities and a failed relationship between the Ca2+-dependent F1FO-ATPase and the mPTP in mussels. The findings suggest that mPTP role and regulation may be different in different taxa and that the F1FO-ATPase insensitivity to NaHS may allow mussels to cope with environmental sulfide.

Phenylglyoxal inhibition of the mitochondrial F1FO-ATPase activated by Mg2+ or by Ca2+ provides clues on the mitochondrial permeability transition pore.

Phenylglyoxal (PGO), known to cause post-translational modifications of Arg residues, was used to highlight the role of arginine residues of the F1FO-ATPase, which may be crucial to yield the mitochondrial permeability transition pore (mPTP). In swine heart mitochondria PGO inhibits ATP hydrolysis by the F1FO-ATPase either sustained by the natural cofactor Mg2+ or by Ca2+ by a similar uncompetitive inhibition mechanism, namely the tertiary complex (ESI) only forms when the ATP substrate is already bound to the enzyme, and with similar strength, as shown by the similar K'i values (0.82 ± 0.07 mM in presence of Mg2+ and 0.64 ± 0.05 mM in the presence of Ca2+). Multiple inhibitor analysis indicates that features of the F1 catalytic sites and/or the FO proton binding sites are apparently unaffected by PGO. However, PGO and F1 or FO inhibitors can bind the enzyme combine simultaneously. However they mutually hinder to bind the Mg2+-activated F1FO-ATPase, whereas they do not mutually exclude to bind the Ca2+-activated F1FO-ATPase. The putative formation of PGO-arginine adducts, and the consequent spatial rearrangement in the enzyme structure, inhibits the F1FO-ATPase activity but, as shown by the calcium retention capacity evaluation in intact mitochondria, apparently favours the mPTP formation.

Season and Cooking May Alter Fatty Acids Profile of Polar Lipids from Blue-Back Fish.

Polar lipids (PoL) represent a new promising dietary approach in the prevention and treatment of many human diseases, due to their potential nutritional value and unique biophysical properties. This study investigates the effects of catching season and oven baking on the fatty acid profiles (FAP) of PoL in four species of blue-back fish widely present in the North Adriatic Sea: anchovy (Engraulis encrasicholus), sardine (Sardina pilchardus), sprat (Sprattus sprattus), and horse mackerel (Trachurus trachurus). PoL levels (427-652 mg/100 g flesh) varied among the four species, with no significant seasonal variations within species. FAP of raw fillets were particularly high in polyunsaturated fatty acid (PUFA), especially docosahexaenoic acid (DHA) and EPA; total PUFA was constant in all species throughout the year, while long-chain n-3 polyunsaturated fatty acid (n-3 PUFA) rose in spring (except in sprat), especially due to the contribution of DHA. The FAP response for PoL to oven baking was species-specific and, among n-3 PUFA, DHA exhibited the greatest heat resistance; the influence of oven baking on FAP was found to be correlated with the catching season, especially for anchovy and sardine, while sprat PoL were not affected by cooking processes. The four species analyzed in this study presented very low n-6/n-3 fatty acid ratios and highly favorable nutritional indices, emphasizing their PoL qualities and promoting their role in increasing human n-3 PUFA intake. The four species can be considered as superior sources of n-3 PUFA and can be employed as supplements in functional food manufacturing and in pharmaceutical and cosmetic industries.

Mitochondrial Ca2+ -activated F1 FO -ATPase hydrolyzes ATP and promotes the permeability transition pore.

The properties of the mitochondrial F1 FO -ATPase catalytic site, which can bind Mg2+ , Mn2+ , or Ca2+ and hydrolyze ATP, were explored by inhibition kinetic analyses to cast light on the Ca2+ -activated F1 FO -ATPase connection with the permeability transition pore (PTP) that initiates cascade events leading to cell death. While the natural cofactor Mg2+ activates the F1 FO -ATPase in competition with Mn2+ , Ca2+ is a noncompetitive inhibitor in the presence of Mg2+ . Selective F1 inhibitors (Is-F1 ), namely NBD-Cl, piceatannol, resveratrol, and quercetin, exerted different mechanisms (mixed and uncompetitive inhibition) on either Ca2+ - or Mg2+ -activated F1 FO -ATPase, consistent with the conclusion that the catalytic mechanism changes when Mg2+ is replaced by Ca2+ . In a partially purified F1 domain preparation, Ca2+ -activated F1 -ATPase maintained Is-F1 sensitivity, and enzyme inhibition was accompanied by the maintenance of the mitochondrial calcium retention capacity and membrane potential. The data strengthen the structural relationship between Ca2+ -activated F1 FO -ATPase and the PTP, and, in turn, on consequences, such as physiopathological cellular changes.

Characterization of metabolic profiles and lipopolysaccharide effects on porcine vascular wall mesenchymal stem cells.

The link between metabolic remodeling and stem cell fate is still unclear. To explore this topic, the metabolic profile of porcine vascular wall mesenchymal stem cells (pVW-MSCs) was investigated. At the first and second cell passages, pVW-MSCs exploit both glycolysis and cellular respiration to synthesize adenosine triphosphate (ATP), but in the subsequent (third to eighth) passages they do not show any mitochondrial ATP turnover. Interestingly, when the first passage pVW-MSCs are exposed to 0.1 or 10 µg/ml lipopolysaccharides (LPSs) for 4 hr, even if ATP synthesis is prevented, the spare respiratory capacity is retained and the glycolytic capacity is unaffected. In contrast, the exposure of pVW-MSCs at the fifth passage to 10 µg/ml LPS stimulates mitochondrial ATP synthesis. Flow cytometry rules out any reactive oxygen species (ROS) involvement in the LPS effects, thus suggesting that the pVW-MSC metabolic pattern is modulated by culture conditions via ROS-independent mechanisms.

Crucial aminoacids in the FO sector of the F1FO-ATP synthase address H+ across the inner mitochondrial membrane: molecular implications in mitochondrial dysfunctions.

The eukaryotic F1FO-ATP synthase/hydrolase activity is coupled to H+ translocation through the inner mitochondrial membrane. According to a recent model, two asymmetric H+ half-channels in the a subunit translate a transmembrane vertical H+ flux into the rotor rotation required for ATP synthesis/hydrolysis. Along the H+ pathway, conserved aminoacid residues, mainly glutamate, address H+ both in the downhill and uphill transmembrane movements to synthesize or hydrolyze ATP, respectively. Point mutations responsible for these aminoacid changes affect H+ transfer through the membrane and, as a cascade, result in mitochondrial dysfunctions and related pathologies. The involvement of specific aminoacid residues in driving H+ along their transmembrane pathway within a subunit, sustained by the literature and calculated data, leads to depict a model consistent with some mitochondrial disorders.

Lipid-protein interactions in mitochondrial membranes from bivalve mollusks: molecular strategies in different species.

The mitochondrial F1FO-ATPase, the key enzyme in cell bioenergetics, apparently works in the same way in mollusks and in mammals. We previously pointed out a raft-like arrangement in mussel gill mitochondrial membranes, which apparently distinguishes bivalve mollusks from mammals. To explore the relationship between the microenvironmental features and the enzyme activity, the physico-chemical features of mitochondrial membranes and the F1FO-ATPase activity temperature-dependence are here explored in the Manila clam (Ruditapes philippinarum). Similarly to the mussel, clam gill mitochondrial membrane lipids exhibit a high sterol content (42 mg/g protein), mainly due to phytosterols (cholesterol only attains 42% of total sterols), and abundant polyunsaturated fatty acids (PUFA) (70% of total fatty acids), especially of the n-3 family. However, the F1FO-ATPase activation energies above and below the break in the Arrhenius plot (22.1 °C) are lower than in mussel and mammalian mitochondria. Laurdan fluorescence spectroscopy analyses carried out at 10 °C, 20 °C and 30 °C on mitochondrial membranes and on lipid vesicles obtained from total lipid extracts of mitochondria, indicate a physical state without coexisting domains. This mitochondrial membrane constitution, allowed by lipid-lipid and lipidprotein interactions and involving PUFA-rich phospholipids, phytosterols (much more diversified in clams than in mussels) and proteins, enables the maintenance of a homogeneous physical state in the range 10-30 °C. Consistently, this molecular interaction network would somehow extend the temperature range of the F1FO-ATPase activity and may contribute to clam resilience to temperature changes.

From the Ca2+-activated F1FO-ATPase to the mitochondrial permeability transition pore: an overview.

Based on recent advances on the Ca2+-activated F1FO-ATPase features, a novel multistep mechanism involving the mitochondrial F1FO complex in the formation and opening of the still enigmatic mitochondrial permeability transition pore (MPTP), is proposed. MPTP opening makes the inner mitochondrial membrane (IMM) permeable to ions and solutes and, through cascade events, addresses cell fate to death. Since MPTP forms when matrix Ca2+ concentration rises and ATP is hydrolyzed by the F1FO-ATPase, conformational changes, triggered by Ca2+ insertion in F1, may be transmitted to FO and locally modify the IMM curvature. These events would cause F1FO-ATPase dimer dissociation and MPTP opening.

The inhibition of the mitochondrial F1FO-ATPase activity when activated by Ca2+ opens new regulatory roles for NAD.

The mitochondrial F1FO-ATPase is uncompetitively inhibited by NAD+ only when the natural cofactor Mg2+ is replaced by Ca2+, a mode putatively involved in cell death. The Ca2+-dependent F1FO-ATPase is also inhibited when NAD+ concentration in mitochondria is raised by acetoacetate. The enzyme inhibition by NAD+ cannot be ascribed to any de-ac(et)ylation or ADP-ribosylation by sirtuines, as it is not reversed by nicotinamide. Moreover, the addition of acetyl-CoA or palmitate, which would favor the enzyme ac(et)ylation, does not affect the F1FO-ATPase activity. Consistently, NAD+ may play a new role, not associated with redox and non-redox enzymatic reactions, in the Ca2+-dependent regulation of the F1FO-ATPase activity.

Post-translational modifications of the mitochondrial F1FO-ATPase.

BACKGROUND: The mitochondrial F1FO-ATPase has the main role in synthesizing most of ATP, thus providing energy to living cells, but it also works in reverse and hydrolyzes ATP, depending on the transmembrane electrochemical gradient. Within the same complex the vital role of the enzyme of life coexists with that of molecular switch to trigger programmed cell death. The two-faced vital/lethal role makes the enzyme complex an intriguing biochemical target to fight pathogens resistant to traditional therapies and diseases linked to mitochondrial dysfunctions. A variety of post-translational modifications (PTMs) of selected F1FO-ATPase aminoacids have been reported to affect the enzyme function. SCOPE OF REVIEW: By reviewing the known PTMs of aminoacid side chains of both F1 and FO sectors according to the most recent advances, the main aim is to highlight how local chemical changes may constitute the molecular key leading to pathological or physiological events. MAJOR CONCLUSIONS: PTMs represent the chemical tool to modulate the F1FO-ATPase activity in response to different stimuli. Some PTMs are required to ensure the enzyme catalysis or, conversely, to inactivate the enzyme function. Each covalent modification of the F1FO-ATPase, which occur in response to local changes, is the result of a selective molecular mechanism which, by translating a chemical modification into a biochemical effect, guarantees the enzyme tuning under changing conditions. GENERAL SIGNIFICANCE: Once highlighted how the molecular mechanism works, some PTMs may be exploited to modulate the effect of drugs targeting the enzyme complex or constitute promising tools for F1FO-ATPase-targeted therapeutic strategies.

Kinetic properties of the mitochondrial F1FO-ATPase activity elicited by Ca2+ in replacement of Mg2.

The mitochondrial F-ATPase can be activated either by the classical cofactor Mg2+ or, with lower efficiency, by Ca2+. The latter may play a role when calcium concentration rises in mitochondria, a condition associated with cascade events leading to cell death. Common and distinctive features of these differently activated mitochondrial ATPases were pointed out in swine heart mitochondria. When Ca2+ replaces the natural cofactor Mg2+, the enzyme responsiveness to the transmembrane electrochemical gradient and to the classical F-ATPase inhibitors DCCD and oligomycin as well as the oligomycin sensitivity loss by thiol oxidation, are maintained. Consistently, the two mitochondrial ATPases apparently share the F1FO complex basic structure and mechanism. Peculiar cation-dependent properties, which may affect the F1 catalytic mechanism and/or the FO proton binding site features, may be linked to a different physiological role of the mitochondrial Ca-activated F-ATPase with respect to the Mg-activated F-ATPase.

Mercury and protein thiols: Stimulation of mitochondrial F1FO-ATPase and inhibition of respiration.

In spite of the known widespread toxicity of mercury, its impact on mitochondrial bioenergetics is a still poorly explored topic. Even if many studies have dealt with mercury poisoning of mitochondrial respiration, as far as we are aware Hg2+ effects on individual complexes are not so clear. In the present study changes in swine heart mitochondrial respiration and F1FO-ATPase (F-ATPase) activity promoted by micromolar Hg2+ concentrations were investigated. Hg2+ was found to inhibit the respiration of NADH-energized mitochondria, whereas it was ineffective when the substrate was succinate. Interestingly, the same micromolar Hg2+ doses which inhibited the NADH-O2 activity stimulated the F-ATPase, most likely by interacting with adjacent thiol residues. Accordingly, Hg2+ dose-dependently decreased protein thiols and all the elicited effects on mitochondrial complexes were reversed by the thiol reducing agent DTE. These findings clearly indicate that Hg2+ interacts with Cys residues of these complexes and differently modulate their functionality by modifying the redox state of thiol groups. The results, which cast light on some implications of metal-thiol interactions up to now not fully explored, may contribute to clarify the molecular mechanisms of mercury toxicity to mitochondria.

Deleterious effects of tributyltin on porcine vascular stem cells physiology.

The vascular functional and structural integrity is essential for the maintenance of the whole organism and it has been demonstrated that different types of vascular progenitor cells resident in the vessel wall play an important role in this process. The purpose of the present research was to observe the effect of tributyltin (TBT), a risk factor for vascular disorders, on porcine Aortic Vascular Precursor Cells (pAVPCs) in term of cytotoxicity, gene expression profile, functionality and differentiation potential. We have demonstrated that pAVPCs morphology deeply changed following TBT treatment. After 48h a cytotoxic effect has been detected and Annexin binding assay demonstrated that TBT induced apoptosis. The transcriptional profile of characteristic pericyte markers has been altered: TBT 10nM substantially induced alpha-SMA, while, TBT 500nM determined a significant reduction of all pericyte markers. IL-6 protein detected in the medium of pAVPCs treated with TBT at both doses studied and with a dose response. TBT has interfered with normal pAVPC functionality preventing their ability to support a capillary-like network. In addition TBT has determined an increase of pAVPC adipogenic differentiation. In conclusion in the present paper we have demonstrated that TBT alters the vascular stem cells in terms of structure, functionality and differentiating capability, therefore effects of TBT in blood should be deeply explored to understand the potential vascular risk associated with the alteration of vascular stem cell physiology.

Preferential nitrite inhibition of the mitochondrial F1FO-ATPase activities when activated by Ca(2+) in replacement of the natural cofactor Mg(2+).

BACKGROUND: The mitochondrial F1FO-ATP synthase has not only the known life function in building most cellular ATP, but also, as recently hinted, an amazing involvement in cell death. Accordingly, the two-faced enzyme complex, which catalyzes both ATP synthesis and ATP hydrolysis, has been involved in the mitochondrial permeability transition, the master player in apoptosis and necrosis. Nitrite, a cellular nitric oxide reservoir, has a recognized role in cardiovascular protection, through still unclear mechanisms. METHODS: In swine heart mitochondria the effect of nitrite on the F1FO-ATPase activity activated by Ca(2+), henceforth defined as Ca-ATPase(s), or by the natural cofactor Mg(2+), was investigated by evaluating ATP hydrolysis under different assay conditions. RESULTS: Ca(2+) is far less efficient than the natural cofactor Mg(2+) in the ATPase activation. However, when activated by Ca(2+) the ATPase activity is especially responsive to nitrite, which acts as uncompetitive inhibitor and up to 2 mM inhibits the Ca2+-activated-ATPase(s), probably by promoting dytirosine formation on the enzyme proteins, leaving the Mg-ATPase(s) unaffected. Most likely these ATPases refer to the same F1FO complex, even if coexistent ATPases may overlap. CONCLUSIONS: The preferential inhibition by nitrite of the Ca-ATPase(s), due to post-translational tyrosine modifications, may prevent the calcium-dependent functionality of the mitochondrial F1FO complex and related events. GENERAL SIGNIFICANCE: In mitochondria the preferential inhibition of the Ca-ATPase activity/ies by nitrite concentrations which do not affect the coexistent Mg-ATPase(s) may quench the negative events linked to the calcium-dependent functioning mode of the F1FO complex under pathological conditions.

The c-Ring of the F1FO-ATP Synthase: Facts and Perspectives.

The F1FO-ATP synthase is the only enzyme in nature endowed with bi-functional catalytic mechanism of synthesis and hydrolysis of ATP. The enzyme functions, not only confined to energy transduction, are tied to three intrinsic features of the annular arrangement of c subunits which constitutes the so-called c-ring, the core of the membrane-embedded FO domain: (i) the c-ring constitution is linked to the number of ions (H(+) or Na(+)) channeled across the membrane during the dissipation of the transmembrane electrochemical gradient, which in turn determines the species-specific bioenergetic cost of ATP, the "molecular currency unit" of energy transfer in all living beings; (ii) the c-ring is increasingly involved in the mitochondrial permeability transition, an event linked to cell death and to most mitochondrial dysfunctions; (iii) the c subunit species-specific amino acid sequence and susceptibility to post-translational modifications can address antibacterial drug design according to the model of enzyme inhibitors which target the c subunits. Therefore, the simple c-ring structure not only allows the F1FO-ATP synthase to perform the two opposite tasks of molecular machine of cell life and death, but it also amplifies the enzyme's potential role as a drug target.

Lipid unsaturation per se does not explain the physical state of mitochondrial membranes in Mytilus galloprovincialis.

Through a multiple approach, the present study on the mitochondrial membranes from mussel gills and swine heart combines some biochemical information on fatty acid composition, sterol pattern, and temperature dependence of the F1FO-ATPase activity (EC 3.6.3.14.) with fluorescence data on mitochondrial membranes and on liposomes obtained from lipid extracts of mitochondria. The physical state of mussel gills and swine heart was investigated by Laurdan steady state fluorescence. Quite surprisingly, the similar temperature dependence of the F1FO complex, illustrated as Arrhenius plot which in both mitochondria exhibits the same discontinuity at approximately 21°C and overlapping activation energies above and below the discontinuity, is apparently compatible with a different composition and physical state of mitochondrial membranes. Accordingly, mussel membranes contain highly unsaturated fatty acids, abundant sterols, including phytosterols, while mammalian membranes only contain cholesterol and in prevalence shorter and less unsaturated fatty acids, leading to a lower membrane unsaturation with respect to mussel mitochondria. As suggested by fluorescence data, the likely formation of peculiar microdomains interacting with the membrane-bound enzyme complex in mussel mitochondria could produce an environment which somehow approaches the physical state of mammalian mitochondrial membranes. Thus, as an adaptive strategy, the interaction between sterols, highly unsaturated phospholipids and proteins in mussel gill mitochondria could allow the F1FO-ATPase activity to maintain the same activation energy as the mammalian enzyme.