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PubMed1983

Modification of flagellar waveform and adenosine triphosphatase activity in reactivated sea-urchin sperm treated with N-ethylmaleimide.

Treatment of demembranated sea-urchin sperm for 1-2 min with 10 microM-N-ethylmaleimide (Mal-NEt) at pH 8.0 prior to reactivation with 1 mM-ATP causes the asymmetry of the flagellar waveform to become desensitized to the presence or absence of Ca2+ in the reactivating medium. In such sperm, changes in concentration of free Ca2+ between 10(-7) M and 10(-3) M have no effect on the asymmetry of the waveforms as measured by the turning rate of the sperm in radians per beat cycle, while the beat frequency and the propulsive efficiency of the waves remain unchanged from the values observed in control preparations not treated with MalNEt. A somewhat more prolonged treatment with MalNEt causes a progressive decrease in the bend angles of the flagellar waves, while the beat frequency and the wavelength still remain largely unchanged. Further extension of the treatment with MalNEt causes complete loss of motility. Little ATP-induced sliding of the doublet tubules is observed upon treatment with trypsin of sperm flagella that have been rendered non-motile with MalNEt. However, the preparations of solubilized dynein 1 obtained by 0.6 M-NaCl extraction of axonemes treated with MalNEt appear almost identical to those obtained from untreated axonemes, both in terms of the amount solubilized and in the specific ATPase activities of their latent and Triton-activated forms. These preparations also appear capable of restoring much of the beat frequency of dynein-1-depleted flagella. These results suggest that the observed desensitization to Ca2+ and decrease in bend angle result from the reaction of MalNEt with axonemal polypeptides that are not part of the dynein 1 particle extracted with 0.6 M-NaCl. The rate of ATP hydrolysis by demembranated sperm rendered non-motile with MalNEt remains relatively high, and it decreases about 50% when the flagella are broken by brief homogenization. This 'homogenizer-sensitive' ATPase activity appears to be derived from some flagellar regulatory mechanism, which controls the ATPase activity of intact non-motile axonemes.

Adenosine Triphosphatases↗
PubMed1990

N-ethylmaleimide-sensitive protein(s) involved in cortical exocytosis in the sea urchin egg: localization to both cortical vesicles and plasma membrane.

The exocytotic release of secretory products from fragments of sea urchin egg cortex has been shown to be inhibited by covalent modification of membrane sulfhydryl groups with N-ethylmaleimide (NEM). Exocytotically competent preparations of reconstituted cortex, formed by recombination of purified cortical vesicles (CVs) with fragments of egg plasma membrane (PM) were also inhibited by treatment with NEM. The cellular localization of sulfhydryl-containing constituent(s) responsible for inhibition was investigated by treating CVs and/or PM with NEM prior to reconstitution. Both native cortex and cortex reconstituted with NEM-treated components were challenged with calcium-containing buffers. Exocytosis was monitored by phase-contrast microscopy, and quantitated by light scattering. Evidence for CV-PM fusion was obtained with an immunofluorescence-based assay that permits visualization of the transport of CV content proteins across the PM. Cortex reconstituted by recombination of NEM-treated CVs with untreated PM or by recombination of untreated CVs with NEM-treated PM was exocytotically competent, whereas cortex formed by recombination of NEM-treated CVs with NEM-treated PM was inactive. These results: (1) support the hypothesis that the mechanism of exocytosis in native and reconstituted cortex is the same; (2) provide evidence that both CV and plasma membranes participate in the release of CV contents from reconstituted cortex; and (3) suggest that sulfhydryl-containing protein(s) present on the surface of purified CVs and plasma membrane are involved in exocytosis.

Animals↗
PubMed1991

Activation by N-ethylmaleimide of a Cl--dependent K+ flux in isolated trout hepatocytes.

Isolated trout hepatocytes when swollen in hypotonic medium undergo a regulatory volume decrease (RVD), which occurs via KCl loss. The system shows characteristics similar to those of the transporter described in red cells. This led us to investigate, in trout hepatocytes, the effect of another signal known to activate this flux in red cells, i.e. treatment with the sulphhydryl-group reagent N-ethylmaleimide (NEM). NEM treatment resulted in a striking increase in ouabain-resistant K+ uptake measured by an isotope pulse uptake technique. The time course of the response to NEM was similar to that obtained with a hypotonic shock, indicating that the effect of NEM was immediate and transient. The NEM-stimulated K+ influx demonstrated the same anion sensitivity as the volume-induced K+ influx, i.e. a specific requirement for Br- or Cl-. Efflux experiments showed that NEM treatment produced a stimulation of both K+ and Cl- effluxes leading to a substantial net loss (10%) of cellular KCl, as confirmed by analysis of ionic contents. This KCl loss is consistent with the rapid cell shrinkage observed after addition of NEM. The Cl--dependent K+ influx was found to be independent of external Na+; in addition, NEM had no effect on Na+ content, indicating that Na+ is not implicated in this process. The effect of loop diuretics was tested on the NEM-stimulated K+ influx. As observed for the volume-induced K+ flux, a high concentration of furosemide (10(-3) mol l-1) is required for full inhibition of this flux; no effect was obtained with bumetanide (10(-4) mol l-1). Consequently, NEM appears to activate a KCl cotransport similar to the one induced in hypotonically swollen cells. Finally, the combination of the two treatments, NEM and hypotonic shock, was found to increase the K+ fluxes even further, suggesting additivity of the two stimuli by mutual positive interaction.

Animals↗
PubMed2002

In vivo membrane trafficking role for an insect N-ethylmaleimide-sensitive factor which is developmentally regulated in endocrine cells.

The hexameric ATPase, N-ethylmaleimide-sensitive factor (NSF) is implicated in the release of neurotransmitters and in mediating fusion between intracellular membranes. Due to the conservation of proteins in constitutive and regulated membrane fusion reactions, NSF and its downstream targets have been predicted also to participate in fusion reactions underlying endocrine function, but there is little experimental evidence to support such a role for NSF in insect neuroendocrine secretion. Here we have characterized the NSF orthologue (MsNSF) from the endocrine model for development Manduca sexta. MsNSF is developmentally regulated in endocrine organs of the protocerebral complex. Enrichment of MsNSF in corpora cardiaca (CC) and not in corpora allata (CA) indicates that it might play a preferential role in releasing hormones produced in CC. Endocrine/paracrine cells of the enteric system in M. sexta exhibit selective MsNSF enrichment. Together the data point to a more selective participation of MsNSF in development of M. sexta by its involvement in a subset of factors, whereas other as-yet-unidentified homolog(s) might regulate secretion from CA and a large set of endocrine/paracrine cells. We further characterized the in vivo role of MsNSF by heterologous expression. In contrast to vertebrate NSF, MsNSF is functional in yeast membrane fusion in vivo. MsNSF rectifies defects in SEC18 (yeast NSF homologue) at nearly all discernible steps where Sec18p has been implicated in the biosynthetic route. This underscores the utility of our approach to delineate functional roles for proteins from systems that are not currently amenable to in vitro reconstitution.

Adenosine Triphosphatases↗
PubMed1997

Molecular cloning of the nemA gene encoding N-ethylmaleimide reductase from Escherichia coli.

Using the gene mapping membrane technique, we identified a gene (nemA) that encodes N-ethylmaleimide reductase in Escherichia coli. The open reading frame encodes a polypeptide of 365 amino acids with a molecular mass of 39,514 Da. The deduced amino acid sequence showed a high degree of homology (87% identical) with the pentaerythritol tetranitrate reductase of Enterobacter cloacae and the morphinone reductase of Pseudomonas putida (52% identical).

Amino Acid Sequence↗
PubMedDate not supplied

N-ethylmaleimide-sensitive factor: a redox sensor in exocytosis.

Vascular injury triggers endothelial exocytosis of granules, releasing pro-inflammatory and pro-thrombotic mediators into the blood. Nitric oxide (NO) and reactive oxygen species (ROS) limit vascular inflammation and thrombosis by inhibiting endothelial exocytosis. NO decreases exocytosis by regulating the activity of the N-ethylmaleimide-sensitive factor (NSF), a central component of the exocytic machinery. NO nitrosylates specific cysteine residues of NSF, thereby inhibiting NSF disassembly of the soluble NSF attachment protein receptor (SNARE). NO also modulates exocytosis of other cells; for example, NO regulates platelet activation by inhibiting alpha-granule secretion from platelets. Other radicals besides NO can regulate exocytosis as well. For example, H(2)O(2) inhibits exocytosis by oxidizing NSF. Using site-directed mutagenesis, we have defined the critical cysteine residues of NSF, and found that one particular cysteine residue, C264, renders NSF sensitive to oxidative stress. Since radicals such as NO and H(2)O(2) inhibit NSF and decrease exocytosis, NSF may act as a redox sensor, modulating exocytosis in response to changes in oxidative stress.

Animals↗
PubMed1998

Lack of function of an N-ethylmaleimide-sensitive thiol protein in erythrocyte membrane of autosomal dominant polycystic kidney disease.

The polycystic kidney disease 1 (PKD1) gene product polycystin has been predicted to be an integral membrane protein involved in cell-cell and cell-matrix interactions. The erythrocyte membrane fluidity in autosomal dominant polycystic kidney disease (ADPKD) patients is increased, and this may be due to a membrane cytoskeletal abnormality. The abnormal erythrocyte sodium-lithium countertransport kinetics in-ADPKD are related to an altered thiol protein in the cytoskeleton. The possibility that a similar thiol protein abnormality causes the increased erythrocyte membrane fluidity in ADPKD was investigated. The membrane fluidity of intact erythrocytes from 12 ADPKD patients and 12 healthy control subjects was assessed from the fluorescence anisotropies of 1,6-diphenyl-1,3,5-hexatriene (DPH) and trimethylammonium-diphenyl-hexatriene (TMA-DPH). The effect on membrane fluidity of N-ethylmaleimide (NEM), cytochalasin D, heating at 48 degrees C for 20 min, or more specifically, liposomes containing antibodies to actin or ankyrin, was determined. In erythrocytes from healthy control subjects, the fluorescence anisotropy of DPH (mean +/- SEM: 0.223 +/- 0.001) was decreased after treatment with NEM (0.200 +/- 0.003, P < 0.001), cytochalasin D (0.206 +/- 0.006, P < 0.001), heating (0.199 +/- 0.002, P < 0.001), and antibodies to actin (0.194 +/- 0.002, P < 0.001) or ankyrin (0.196 +/- 0.002, P < 0.001). The TMA-DPH anisotropy (0.279 +/- 0.001) was also decreased after treatment with NEM (0.264 +/- 0.001, P < 0.001), cytochalasin D (0.264 +/- 0.001, P < 0.001), heating (0.265 +/- 0.001, P < 0.001), and antibodies to actin (0.262 +/- 0.002, P < 0.001) or ankyrin (0.262 +/- 0.002, P < 0.001). NEM had no additional effect on the other treatments, suggesting that its target thiol protein was associated with the cytoskeleton. In untreated erythrocytes from ADPKD patients, fluorescence anisotropies of both DPH and TMA-DPH were reduced, and none of the treatments altered the anisotropy of either DPH or TMA-DPH. In ADPKD, a cytoskeletal thiol protein is abnormal and possibly explains abnormal lipid bilayer properties and transport protein function in erythrocytes in this disease.

Actins↗
PubMed1978

The action of N-ethylmaleimide on the membrane currents and contractile tension in the bullfrog atrium.

The effects of N-ethylmaleimide (NEM), a sulfhydryl blocking reagent, on the membrane currents, action potentials and contractile tension in bullfrog atrial muscle were studied by using the double sucrose gap technique. In concentrations of 10(-3) to 10(-4) M, NEM led to a transient enhancement of twitch contraction followed by a late inhibition, while 10(-2) M NEM merely produced an inhibitory effect. The positive inotropism was accompanied by a prolongation of action potential and the negative inotropism, by a depression of action potential. Under voltage clamp conditions, 10(-3) M NEM reduced the fast inward current and increased the steady state outward and background currents. The slow inward current and the inward Ca current in Na-free conditions were transiently increased by 10(-3) M NEM with an enhancement of contractile tension. In voltage-tension relationships, NEM-induced augmentation of tension appeared in depolarizing pulses of 60--70 mV. The results indicate that NEM increases transiently the Ca conductance of the cell membrane. Preincubation with L-cysteine blocked the production of positive inotropic effect by NEM, suggesting that the effects of NEM are due to the blockade of protein sulfhydryl group in the atrial muscle.

Action Potentials↗
PubMed1978

Different effects of N-ethylmaleimide on the tension components of bullfrog atrium.

The effects of N-ethylmaleimide (NEM) on the tension components of bullfrog atrium were studied under voltage clamp conditions using the double sucrose gap technique. NEM at a dilution of 10(-3) M inhibited the ICa-independent tonic tension elicited by large and long depolarizing pulses (140 mV, 2 sec) time-dependently, whereas the drug produced an initial transient increase and a later decrease of the ICa-dependent phasic tension elicited by small and short depolarizing pulses (60 mV, 100 msec). The effect of NEM was facilitated when the atrial muscles were exposed to a solution having either a reduced Na or an increased Ca concentration. In the presence of Mn ions, 10(-3) M NEM did not evidently inhibit tonic tension, and it led to a slight transient increase in phasic tension. NEM at 10(-3) M, which is known to inhibit sarcolemmal Na, K-ATPase, enhanced both the phasic tension and the tonic tension in the presence of ouabain and when perfused with K-free solution. Even under these conditions (10(-3) M NEM caused an initial transient decrease of ICa-independent tonic tension. This suggests that NEM has a different action on the atrial muscle from those of cardiac glycosides such as ouabain.

Animals↗
PubMed1979

The time-dependent and dose-dependent effects of the sulfhydryl blocker N-ethylmaleimide on the tonic tension in bullfrog atrium.

The kinetics of the inhibitory action by N-ethylmaleimide (NEM) on ICa-independent tonic tension in bullfrog atrial muscle was studied under voltage-clamped conditions, using the double sucrose gap method. The higher the concentration of NEM became, the larger was the rate of decrease of the tonic tension. In addition, the tension decreased with time of exposure to NEM. When the rate of the decrease of the tonic tension was plotted as a function of NEM concentration, the curve showed saturation kinetics of the Michaelis-Menten type with respect to NEM concentration, following the characteristics of a carrier-mediated process. Moreover, in the presence of excess Ca or half quantity of Na in Ringer solution, the curve showed sigmoidal kinetics. This probably indicates that the condition of either an excess of Ca or a reduction of Na in Ringer solution is apparently a cooperative effector of the inhibitory action of NEM, suggesting that the carrier protein responsible for the generation of tonic tension may be an allosteric protein. Finally, the relationship between ICa-independent tonic tension and the Na-Ca exchange mechanism which is supposed to be a powerful candidate for generating tension was discussed.

Animals↗
PubMed1990

Effect of N-ethylmaleimide on beef and rat liver vitamin K1 epoxide reductase.

There is little difference in the extent of inactivation of beef liver microsomal vitamin K1 epoxide reductase by N-ethylmaleimide (NEM) whether or not the microsomes are pre-treated with dithiothreitol (DTT). The rat liver microsomal enzyme, however, is inactivated by NEM to a much greater extent if the microsomes are pre-treated with DTT. The beef liver enzyme activity is protected from NEM inactivation by the substrate, vitamin K1 epoxide. Ping-pong kinetics are exhibited by the beef liver enzyme. These results support a mechanism for vitamin K1 epoxide reductase in which the function of the required dithiol is to reduce an active site disulfide bond; however, the geometry of the active sites of the enzyme from rat and beef may be different.

Animals↗
PubMed2000

N-ethylmaleimide-enhanced phosphatidylserine externalization of human pancreatic cancer cells and immediate phosphatidylserine-mediated phagocytosis by macrophages.

The purpose of this study was to examine whether N-ethylmaleimide (NEM) can enhance phosphatidylserine (PS) externalization on the outer surface of cancer cells, and PS-externalized cancer cells can be phagocytosed immediately by macrophages. NEM could externalize PS of cancer cells in concentration- and time-dependent manners. When treated with 5 mM NEM for 1 h, 80% of the carcinoma cells externalized their PS. In phagocytosis assay, these cells were engulfed immediately by macrophages before undergoing apoptosis. These results suggest that NEM can immediately externalize PS of cancer cells, leading to their recognition and phagocytosis by macrophages before undergoing apoptosis morphologically.

Animals↗
PubMed1999

A critical role for N-ethylmaleimide-sensitive fusion protein (NSF) in platelet granule secretion.

The molecular mechanisms that regulate membrane targeting/fusion during platelet granule secretion are not yet understood. N-ethylmaleimide-sensitive fusion protein (NSF), soluble NSF attachment proteins (SNAPs), and SNAREs (SNAP receptors) are elements of a conserved molecular machinery for membrane targeting/fusion that have been detected in platelets. We examined whether NSF, an ATPase that has been shown to play a critical role in membrane targeting/fusion in many cell types, is necessary for platelet granule secretion. Peptides that mimic NSF sequence motifs inhibited both alpha-granule and dense-granule secretion in permeabilized human platelets. This inhibitory effect was sequence-specific, because neither proteinase K-digested peptides nor peptides containing similar amino acids in a scrambled sequence inhibited platelet secretion. The peptides that inhibited platelet granule secretion also inhibited the human recombinant alpha-SNAP-stimulated ATPase activity of recombinant NSF. It was also found that anti-NSF antibodies, which inhibited recombinant alpha-SNAP-stimulated ATPase activity of NSF, inhibited platelet granule secretion in permeabilized cells. The inhibition by anti-NSF antibodies was abolished by the addition of recombinant NSF. These data provide the first functional evidence that NSF plays an important role in platelet granule secretion.

Amino Acid Sequence↗
PubMed1999

Interactions between the thiol-group reagent N-ethylmaleimide and neutral and basic amino acid transporter-related amino acid transport.

The neutral and basic amino acid transport protein (NBAT) expressed in renal and jejunal brush-border membranes is involved in amino acid and cystine absorption. NBAT mutations result in Type 1 cystinuria. A C-terminal myc-tagged NBAT (NBATmyc) retains the amino acid transport and protein-protein interaction properties of NBAT when expressed in Xenopus oocytes. Neutral amino acid (Ala, Phe)-cationic amino acid (Arg) heteroexchanges related to NBATmyc expression in oocytes are inactivated by treatment with the thiol-group reagent N-ethylmaleimide (NEM), although significant Arg-Arg and Ala-Ala homoexchanges persist. Inactivation of heteroexchange activity by NEM is accompanied by loss of >85% of alanine and cystine uptake, with smaller (<50%) inhibition of arginine and phenylalanine uptake. NEM-sensitive cystine uptake and arginine-alanine heteroexchange (system b(0,+) activity) are not expressed by an NBAT truncation mutant (NBATmyc-Sph1) lacking the 13 C-terminal amino acid residues, but the mutant expresses NEM-resistant transport activity (system y(+)L-like) equivalent to that of full-length NBATmyc. The deleted region of NBATmyc-Sph1 contains two cysteine residues (671/683) which may be the targets of NEM action. The synthetic amino acid 2-trifluoromethylhistidine (TFMH) stimulated alanine efflux at pH 7.5 and arginine at pH 5.5, but not vice versa, establishing the existence of distinct pathways for cationic and neutral amino acid homoexchange (TFMH is zwitterionic at pH 7.5 and cationic at pH 5.5). We suggest that NBAT expresses a combination of system b(0,+) and y(+)L-like activities, possibly by interacting with different light-chain subunits endogenous to oocytes (as does the homologous 4F2hc protein). The C-terminus of NBAT may also have an additional, direct role in the mechanism of System b(0,+) transport (the major transport activity that is defective in Type 1 cystinuria).

Amino Acid Sequence↗
PubMed1999

Phenotypic interaction between temperature-sensitive paralytic mutants comatose and paralytic suggests a role for N-ethylmaleimide-sensitive fusion factor in synaptic vesicle cycling in Drosophila.

The temperature-induced paralysis of comatose (comt) mutants of Drosophila is suggestive of a function for N-ethylmaleimide-sensitive fusion factor (NSF) in the CNS. Mutations in the para gene encoding the subunit of the voltage-gated sodium channel also result in a similar phenotype. We show that paralysis in comt flies is activity-dependent, and in the doubly mutant comt para flies comt-like paralysis does not set in until the effects of para are reversed by shifting to permissive temperatures. During recording from the thoracic flight muscles, we observed that comt flies showed a burst of spontaneous activity at restrictive temperature. This has been reported earlier as a unique characteristic of comt paralysis. The comt para double mutant showed this burst of activity not at restrictive but only on shifting back to permissive temperature. The unusual behavior and electrophysiology of the doubly mutant flies reported here indicates a role for NSF in synaptic vesicle cycling.

Animals↗
PubMed2000

N-Ethylmaleimide induces disaggregation of platelets preaggregated by ADP and thrombin and decreases cytoplasmic calcium level.

The effect of N-ethylmaleimide (NEM, 1-200 microM) on ADP- and thrombin-induced platelet aggregation and thrombin-induced increase in intracellular Ca2+ concentration was studied. Addition of NEM to platelets preaggregated with ADP or thrombin induces platelet disaggregation. The anti-aggregant activity of NEM was different for ADP- and thrombin-induced aggregations. At 200 microM concentration, NEM completely disaggregated ADP-induced aggregates and only partially disaggregated thrombin-aggregated platelets. NEM did not influence the thrombin-induced increase in cytoplasmic Ca2+ and had no effect on the basal level of Ca2+ in the cytosol of non-activated platelets. However, NEM decreased the level of thrombin-mobilized Ca2+ in the cytosol of activated platelets. Thus, NEM can induce disaggregation of ADP- and thrombin-preaggregated platelets by activating a system which removes Ca2+ from the platelet cytosol.

Adenosine Diphosphate↗
PubMed2000

Identification of Rab6 as an N-ethylmaleimide-sensitive fusion protein-binding protein.

In this study we show the interaction of N-ethylmaleimide-sensitive fusion protein (NSF) with a small GTP-binding protein, Rab6. NSF is an ATPase involved in the vesicular transport within eukaryotic cells. Using the yeast two-hybrid system, we have isolated new NSF-binding proteins from the rat lung cDNA library. One of them was Rab6, which is involved in the vesicular transport within the Golgi and trans-Golgi network as a Ras-like GTPase. We demonstrated that the N-terminal domain of NSF interacted with the C-terminal domain of Rab6, and these proteins were co-immunoprecipitated from the rat brain extract. This interaction was maintained preferentially in the presence of hydrolysable ATP. Recombinant NSF-His(6) can also bind to C-terminal Rab6-glutathione S-transferase under the conditions to allow the ATP hydrolysis. Surprisingly, Rab6 stimulates the ATPase activity of NSF by approx. 2-fold as does alpha-soluble NSF attachment protein receptor. Anti-Rab6 polyclonal antibodies significantly inhibited the Rab6-stimulated ATPase activity of NSF. Furthermore, we found that Rab3 and Rab4 can also associate with NSF and stimulate its ATPase activity. Taken together, we propose a model in which Rab can form an ATP hydrolysis-regulated complex with NSF, and function as a signalling molecule to deliver the signal of vesicle fusion through the interaction with NSF.

Adenosine Triphosphate↗
PubMed1975

Phosphate transport in rat liver mitochondria. Membrane components labeled by N-ethylmaleimide during inhibition of transport.

N-ethylmaleimide (NEM) inhibits the transport of phosphate in mitochondria but is without effect on permeation of other metabolities. In spite of its specificity for inhibition of phosphate transport, NEM reacts in an unspecific manner with inner membrane proteins in general. Treatment of mitochondria with [3H]NEM just sufficient to produce inhibition of phosphate transport results in labeling of at least 10 polypeptide components of the inner membrane. A marked increase in the specificity of reaction of NEM for components of the phosphate transport system is attained by first protecting the transport system with p-mercuribenzoate (p-MB) and then by irreversibly blocking reactive sulfhydryl groups unassociated with transport by the addition of unlabeled NEM. Subsequent addition of dithiothreitol removes p-MB and restores 65 to 75 percent of the original phosphate transport activity. Reinhibition of transport with [3H]NEM results in both a 6-fold decrease in the amount of [3H]NEM bound by purified inner membrane vesicles and a substantial reduction in the number of labeled polypeptide components. Five distinct labeled species are detected by this method, one of which is a 32,000 molecular weight protein containing 40 percent of the bound radioactivity, or approximately 160 pmol/mg of inner membrane protein. Correlation of binding of [3H]NEM by inner membrane proteins with inhibition of phosphate transport suggests that the maximum concentration of the NEM-sensitive component of the phosphate transport system is 60 pmol/mg of mitochondrial protein. This value, when combined with V-max of NEM-sensitive transport of 205 nmol times min-1 times mg-1 at O degrees (Coty, W. A., and Pedersen, P. L. (1974) J. Biol. Chem. 249, 2593) yields an approximate minimum turnover for this process of 3500 min-1 at 0 degrees. This turnover number is at least 20-fold greater than similarly calculated values for adenine nucleotide transport and succinate oxidation in rat liver mitochondria at this temperature. Taken together these results suggest that the NEM-sensitive phosphate transport system in rat liver mitochondria has an unusually high catalytic activity compared to other mitochondrial processes, and that at least one of the five NEM-binding proteins is likely to be an essential component of this transport system.

Animals↗