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PubMed1977

A protonmotive force as the source of energy for galactoside transport in energy depleted Escherichia coli.

An artificially produced electrochemical potential difference for protons (portonmotive force) provided the energy for the transport of galactosides in Escherichia coli cells which were depleted of their endogenous energy reserves. The driving force for the entry of protons was provided by either a transmembrane pH gradient or a membrane potential. The pH gradient across the membrane was created by acidifying the external medium. The membrane potential (inside negative) was established by the outward diffusion of potassium (in the presence of valinomycin) or by the inward diffusion of the permeant thiocyanate ion. The magnitude of the electrochemical potential difference for protons agreed well with magnitude of the chemical potential difference of the lactose analog, thiomethylgalactoside. The observations are consistent with the view that the carrier-mediated entry of each galactoside molecule is accompanied by the entry of one proton.

Adenosine Triphosphate↗

PubMed2026

Acute and chronic effects of mixed nuts on energy metabolism in women at cardiometabolic risk: a randomized clinical trial.

BACKGROUND AND AIMS: The effect of consuming a mix of Brazilian nuts on energy metabolism has not been explored. Thus, the present study aimed to evaluate the effects of acute and chronic consumption of mixed nuts on markers of energy metabolism in women with overweight/obesity. METHODS AND RESULTS: This is a randomized, controlled, and parallel clinical trial with adult women. In an acute study, participants received a beverage containing mixed nuts (30 g of cashew nuts + 15 g of Brazil nuts) or a control beverage, and energy metabolism markers were assessed for up to 3 h postprandially. For the chronic study, participants received 45 g of a mix of nuts/day and a -500kcal energy-restricted diet (MNG) or only a -500kcal energy-restricted diet free of nuts (CTG) for 8 weeks, and energy metabolism was assessed before and after the intervention period. In the postprandial period, fat oxidation was higher in the MNG than in the CTG (piAUC: 47.53 ± 5.78 mg/min vs. 27.93 ± 6.98 mg/min; p = 0.048). After 8 weeks of the intervention, fasting fat oxidation increased in the MNG (+16.0 ± 7.0 mg/min) and decreased in the CTG (-5.0 ± 6.0 mg/min), with no significant difference between groups. Other acute and chronic markers also showed no significant changes between groups. CONCLUSION: The acute consumption of mixed nuts increased postprandial fat oxidation, whereas chronic intake within an energy-restricted diet did not affect energy metabolism markers in women at cardiometabolic risk. REGISTRATION NUMBER FOR BRAZILIAN REGISTRY OF CLINICAL TRIALS: RBR-3ntxrm.

Humans↗

PubMed1977

Stabilization of adenylate energy charge and its relation to human sperm motility.

The adenylate energy charge of human ejaculated spermatozoa was studied when the sperm motility was perturbed by varying pH, prolonged incubation, and caffeine. Between pH 8 and 9, which was optimal for the sperm motility, the energy charge was in the physiological range of 0.8 to 0.9. Above pH 9, the mobility, ATP content, and adenine nucleotide pool declined rapidly but the energy charge was maintained slightly below 0.8. Below pH 8, the motility also dropped drastically, but the ATP, nucleotide pool, and energy charge fell only slightly. Prolonged incubations of the spermatozoa decreased the motility, ATP, and nucleotide pool. However, the energy charge would remain above 0.6. Caffeine stimulation of the motility caused a rapid fall of ATP and the reduction of the physiological energy charge by 0.2 unit, unless glucose was added. Imidazole which reduced the caffeine-stimulated motility did not alter the physiological energy charge of the spermatozoa. The study showed that the spermatozoa could maintain the energy charge above 0.6 under stress.

Adenine Nucleotides↗

PubMed2026

An expanded breakfast buffet increases daily energy and protein intakes in hospitalised patients: A prospective crossover quality improvement study.

BACKGROUND & AIMS: Inadequate dietary intake remains common during hospitalisation. Ordinary hospital meals are central to nutritional intake, but their contribution depends on what is offered and what patients are able and willing to eat. We evaluated whether a preference-informed, limited expansion of the hospital breakfast buffet could increase total daily energy and protein intakes. METHODS: This prospectively structured, ward-based crossover quality-improvement study was conducted in seven inpatient wards at a tertiary university hospital. Each ward was observed for four consecutive days and randomly allocated to begin with standard or expanded breakfast, after which conditions alternated daily. The expanded buffet consisted of standard breakfast supplemented with familiar energy- and protein-rich foods selected from previous patient-choice data. Twenty-four-hour intake was registered using component-level weighed food records during the day and nursing registration overnight. Primary outcomes were total daily energy and protein intakes. Linear mixed-effects models adjusted for observation day and ward-level starting sequence and accounted for repeated patient observations and ward-level clustering. Analyses used data from patients who consumed breakfast and contributed analysable observations under both breakfast conditions. RESULTS: The primary crossover population included 71 patients contributing 188 analysable patient-days. Compared with standard breakfast, the expanded breakfast increased total daily energy intake by +198 kcal/day (95% CI 44 to 352) and protein intake by +6.8 g/day (95% CI 1.0 to 12.5), without a statistically significant increase in total food weight. Daily energy and protein adequacy increased by +8.7 and + 6.8 percentage points, respectively. The increase was driven mainly by breakfast intake, with no measurable reduction in non-breakfast intake. CONCLUSIONS: A limited expansion of the ordinary hospital breakfast buffet increased total daily energy and protein intakes in the primary crossover population of hospitalised adults who consumed breakfast. This increase occurred without a statistically significant increase in total food weight or a measurable reduction in non-breakfast intake. Small, preference-informed additions of familiar energy- and protein-rich foods at breakfast may improve daily intake by increasing the nutrient yield of foods patients are able or willing to eat.

Humans↗

PubMedDate not supplied

[Energy characteristics of the stages of photo-dependent transport of 14C-alanine in Halobacterium halobium R1 cells].

The energy of light is utilized by Halobacterium halobium R1 only at the very beginning of illumination at the same time as the transport of protons into the cells, as follows from comparing the data of photophosphorylation and light-dependent transport. The release of protons by the cells on further illumination suggests that the photoprocess and the accumulation of energy by the cells are being uncoupled. The primary transport of 15C-alanine in the course of illumination is caused directly by electrochemical gradient (i) whereas the secondary transport in the dark involves the energy liberated on hydrolysis of ATP which has been formed in the process of photophosphorylation (II). An indirect technique of assaying ATP from the transport of 14C-alanine into the cells makes it possible to characterize the distribution of utilized light energy between photophosphorylation (II) and transport processes (I). The bulk of energy is accumulated as ATP. The incorporation of 14C-alanine into the cells is stimulated twofold by illumination for a long time under physiological conditions in the presence of respiration. Therefore, light plays an important role in the energy balance of H. halobium R1.

Adenosine Triphosphate↗

PubMed1976

Conformational changes in cytochrome aa3 and ATP synthetase of the mitochondrial membrane and their role in mitochondrial energy transduction.

1. The thermodynamics and molecular basis of energy-linked conformational changes in the cytochrome aa3 and ATP synthetase complexes of the mitochondrial membrane have been studied with spectrophotometrical and fluorometrical techniques. 2. Ferric cytochrome aa3 exists in two conformations, high spin and low spin, the equilibrium between these states being controlled by the electrical potential difference across the mitochondrial membrane. The conformational change is brought about by an electrical field-driven binding of one proton per aa3 to the complex. At pH 7.2 the concentration of the two conformations is equal at a membrane potential of 170 mV corresponding to about 4 kcal/mole. 3. The high to low spin transition in ferric aa3 is also induced by hydrolysis of ATP in which case two molecules of aa3 are shifted per ATP molecule hydrolyzed. This is in accordance with translocation of two protons across the mitochondrial membrane coupled to hydrolysis of ATP as proposed in the chemiosmotic theory of oxidative phosphorylation. 4. The conformational transition in cytochrome aa3 is not an expression of the formation of a 'high-energy' intermediate or reversal of the energy-transducing pathway of oxidative phosphorylation, but is presumably the basis of allosteric control of the activity of cytochrome oxidase by the energy state of the mitochondrion. This control is exerted by a regulatory mechanism in which the electrical potential difference controls the conformation and redox properties of the heme centres and thereby the rate of oxygen consumption. 5. The synthesis of one molecule of ATP by oxidative phosphorylation is energetically equivalent to the work done in carrying two electrical charges across the entire mitochondrial membrane. 6. Fluorescence changes of aurovertin bound to ATP synthetase reveal that the electrical membrane potential induces a conformational change in the F1 portion of the enzyme which is probably associated with dissociation of the natural F1 inhibitor protein. This conformational change is energetically equivalent to the work done in carrying one electrical charge across the mitochondrial membrane. 7. A model is proposed for the mechanism of the electrical field-induced conformational changes in the cytochrome aa3 and ATP synthetase complexes, and the significance of these changes in the mechanism and control of mitochondrial energy conservation is discussed.

Adenosine Diphosphate↗

PubMed1978

Sidedness of inhibition of energy transduction in oxidative phosphorylation in rat liver mitochondria by ethidium bromide.

Ethidium bromide, a new type of inhibitor of energy transduction in oxidative phosphorylation, inhibited ATP synthesis in intact mitochondria but not in submitochondrial particles, the latter being inside-out relative to the membranes of intact mitochondria. Ethidium bromide incorporated inside the submitochondrial particles inhibited ATP synthesis in the particles. The decrease of the membrane potential by valinomycin (plus KCl) inhibited only slightly the energy-dependent binding of ethidium bromide to the mitochondria. The present results show clearly that ethidium bromide inhibited energy transduction in oxidative phosphorylation by acting on the outer side (C-side) of the inner mitochondrial membrane, perhaps by neutralizing negative charges created on the surface of the C-side, and that it had no inhibitory activity on the inner side (M-side) of the membrane. Th present results show also that the energy-dependent binding of ethidium is not due to electrophoretic transport down the membrane potential; ethidium may bind to negative charges on the surface of the C-side. The present study suggest that an anisotropic distribution of electric charge in the inner mitochondrial membrane is an intermediary high energy state of oxidatvie phosphorylation.

Adenosine Triphosphate↗

PubMed1975

Hypothesis on the role of liganded states of proteins in energy transducing systems.

In energy transducing systems the direction of energy transfer is proposed to be maintained by the synchronized turnovers of the conformational change of one protein coupling up to affect another. Catalysis by those systems implies, therefore, that under new space restrictions the groups of the transducing enzyme increase and decrease reactivity between themselves, with activatory and/or inhibitory ligands (H+, H2O, metals, etc.) and with the electron shells of the reactant molecules. The exergonic reaction-dependent turnover of the forms of the enzyme within the transition complexes would be maintained, therefore, under asymmetric phase angles of conformational-dependent reactivity that would effectively restrict the microscopic reversibility of transducing systems. Some well known reactions, such as hemoglobins Bohr effect, can be used to illustrate that microscopic (molecular) interactions subject to thermodynamic equilibria laws may similarly paricipate as driving forces in energy transducing sytems. This would allow the thermodynamic description of the role of proton translocation as that of a modificatory force of the structural parameters of proteins. Similarly, the relationship between the liganded states of hemoglobin and its change in conformation has been used to develop an illustrative model relating changes in oxido-reduction of electron carriers to induced-fit effects leading to a sequence of ATPase forms in transition complexes which become stabilized as high energy intermediates under the constraints imposed by the membrane of energy transducing organelles.

Adenine Nucleotides↗

PubMed2026

Dual-tasking reveals severity-dependent reorganization of cortical beta energy landscapes in Parkinson's disease.

Dual-task impairment is a hallmark of Parkinson's disease (PD), yet the large-scale neural mechanisms underlying postural-motor interference remain poorly understood. In particular, it is unclear how cortical network dynamics reorganize across disease severity when postural control competes with concurrent task demands. This study investigated EEG-derived beta-band cortical energy landscapes in healthy older adults, early-stage PD, and mid-stage PD during single- and dual-task conditions. Dual-task behavioral cost increased with disease severity for concurrent manual performance (p < 0.001), whereas a quadratic pattern was observed for postural performance. Energy landscape analysis revealed severity-dependent reconfiguration of cortical beta dynamics. Dual-task-related landscape changes in effective network flexibility (ΔNeff), landscape geometry (ΔEvar and ΔGmag), and dominant low-energy attractor organization (ΔLow mass and ΔLow area) showed significant monotonic trends (p < 0.05), reflecting progressive constrained cortical network dynamics with advancing PD severity. In addition, dual-task-related landscape alterations were associated with clinical severity, as indexed by Hoehn and Yahr stage (|r| = 0.353-0.423, p = 0.016-0.048), and showed associations with motor impairment, as measured by MDS-UPDRS part III scores (|r| = 0.333-0.455, p = 0.009-0.063). These findings demonstrate that dual-task demands induce severity-dependent reconfiguration of cortical beta energy landscapes in PD. Energy landscape geometry may capture systems-level neural constraints associated with dual-task susceptibility in PD, providing a physiologically grounded framework to characterize disease-related functional vulnerability.

Humans↗

PubMed1976

Efficiency of oxidative phosphorylation and energy dissipation by H+ ion recycling in rat-liver mitochondrial metabolizing pyruvate.

A method was developed for the calculation of metabolic fluxes through individual enzymatic reactions of pyruvate metabolism including the citric acid cycle in rat liver mitochondrial incubated at metabolic states between state 4 and state 3. This method is based on the measurement of the specific radioactivities of the products formed from [2-14C]pyruvate. With this procedure the energy balance of mitochondria incubated in the presence of [2-14C]pyruvate, ATP, bicarbonate and phosphate at different ATP/ADP ratios in the medium was calculated. The ATP/ADP ratios were maintained at a steady state with creatine kinase plus creatine as a phosphoryl acceptor. The calculations revealed that by adding increasing concentrations of creatine up to 20 mM the energy dissipated by the mitochondria decreased but showed a local maximum at 13mM creatine. Omission of bicarbonate from the medium led to a shift of this maximum. When energy dissipation was minimal the overall P/O ratio was maximal. The amount of energy dissipated was paralleled by the magnitude of the pH gradient across the inner membrane. From these results it was concluded that the recycling of H+ ions which consists of a passive leakage of H+ ions into the matrix and an active extrusion of these ions out of this compartment, is an important energy dissipating process. The H+ ion recycling is thus one of the processes which give rise to the state 4 respiration in mitochondria.

Adenosine Diphosphate↗

PubMed2025

Cooperative contribution of multiple energy substrate pathways to floral thermogenesis in sacred lotus.

Floral thermogenesis in lotus (Nelumbo nucifera) is a highly energy-intensive process, requiring substantial metabolic reconfiguration and substrate input. However, the mechanisms coordinating energy substrate supply during this process remain unclear. Here, we integrated microscale proteomics, time-series transcriptomics, and mitochondrial feeding assays to elucidate the substrate provisioning strategies supporting thermogenesis in lotus receptacles. Proteomic analysis revealed a concerted upregulation of major energy metabolism pathways at the thermogenic initiation stage, accompanied by enhanced expression of energy dissipation-related proteins (alternative oxidase and uncoupling proteins), indicative of a metabolic shift favoring heat production over ATP synthesis. Our results highlight the cooperative contribution of multiple pyruvate sources to mitochondrial respiration. Both the mitochondrial pyruvate carrier (MPC)-mediated cytosolic pyruvate import and the NAD-dependent malic enzyme (NAD-ME)-derived intramitochondrial pyruvate flux were significantly elevated at the thermogenic stage. Notably, isotopic feeding experiments revealed that NAD-ME-derived pyruvate may contribute more substantially than MPC-derived pyruvate under thermogenic conditions, reflecting a highly flexible substrate utilization strategy. In addition, increased expression of alanine aminotransferase (AlaAT) and β-oxidation-related genes suggested that alanine transamination and fatty acid degradation may further expand the respiratory substrate pool. Collectively, this study uncovers a diverse and dynamic landscape of energy substrate supply that underpins heat production in thermogenic lotus tissues. These findings offer insights into how plants coordinate metabolic flexibility to meet the high energetic demands of floral thermogenesis.

Flowers↗

PubMed2026

Exogenous lactate ameliorates Aβ-induced energy deficit and neurotoxicity with increased mitochondrial TCA cycle carbon flux in SH-SY5Y cells.

A growing body of evidence has demonstrated the existence of metabolic dysfunction in neurodegenerative diseases, including Alzheimer's disease (AD), suggesting that deprivation of energy substrates impairs cellular dynamics. As glucose utilization declines in patients with AD, the need for alternative energy sources becomes crucial to sustain neuronal activities and prevent cell death induced by neurotoxic proteins, such as amyloid beta (Aβ) aggregates. In this context, lactate has been investigated as a potential alternative brain energy substrate in several studies, yet its impact on neuronal cells under Aβ-induced toxicity remains unclear. We confirmed significant suppression of energy production-related biological pathways by analyzing brain transcriptomic data of patients with AD. In subsequent in vitro studies, exogenous lactate treatment ameliorated neuron-like cell death caused by Aβ aggregates. Using a 13C stable isotope tracer, we verified cellular lactate uptake and its incorporation into tricarboxylic acid (TCA) cycle in neurons under the neurotoxic condition. 13C metabolic flux analysis further supported these findings by revealing that lactate treatment restored Aβ-suppressed mitochondrial TCA cycle fluxes. These metabolic improvements were accompanied by increased expression of mitochondrial proteins. These findings support lactate shuttling as a mechanism for supplying lactate-derived carbon to mitochondrial energy metabolism, which may improve neuronal resilience under Aβ-induced metabolic stress.NEW & NOTEWORTHY This study shows that lactate treatment attenuates Aβ-induced cell death in neuron-like cells and supports mitochondrial carbon metabolism. Glycolytic hypometabolism was observed in human AD brain transcriptome and Aβ-treated neuron-like cells. We confirmed that lactate replenished mitochondrial energetics, making neurons more resilient to neurotoxicity. Using 13C tracing and metabolic flux analysis, we found that lactate-derived carbon was incorporated into the TCA cycle and that lactate treatment was associated with restoration of Aβ-suppressed mitochondrial fluxes.

Humans↗

PubMed1976

Energy metabolism in respiration-deficient and wild type Chinese hamster fibroblasts in culture.

This paper presents a comparison of energy metabolism in wild type and respiration-deficient Chinese hamster cells. From previous work (DeFrancesco et. al., '75) it was concluded that the mutant satisfies essentially all of its energy requirements from glycolysis and in this study we measure precisely the amount of glucose consumed and lactate produced per milligram increment of protein in exponentially growing cultures. From these measurements we calculate the amount of ATP derived from glycolysis (and hence the total energy requirement for normal proliferation) to be 105 +/- 15 mumoles ATP/delta mg protein in the mutant. It is 63 +/- 10 mumoles ATP/delta mg protein derived from glycolysis in wild type cells. We present evidence that the total energy requirement of wild type cells is similar to that of the mutant suggesting that approximately 40% of the energy requirement is derived from respiration. The oxidation of glutamine appears to be more significant than the complete oxidation of glucose to CO2 in these Chinese hamster fibroblasts. The amount of ATP required by the mutant cells per milligram increment of protein is relatively independent of pH.

Adenosine Triphosphate↗

PubMed1977

Light energy conservation processes in Halobacterium halobium cells.

In Halobacterium halobium, proton pumping driven by light or by respiration generates an electrochemical potential difference across the membrane. Energy storage in this form is only transient. Cellular energy transducers competing with proton leaks stabilize this free energy as high energy phosphate bonds, electrochemical potential of other ions, and chemical potential of amino acids and possibly other chemical species. The pH changes induced by light or by respiration in cell suspensions are complicated by proton flows associated with the functioning of the cellular energy transducers. Dominant is the proton inflow coupled to the synthesis of ATP, which has been kinetically resolved. A proton-per-ATP ratio of about 3 is calculated from simultaneous measurements of photophosphorylation and the proton inflow. This value is compatible with the chemiosmotic coupling hypothesis. The time course of the light-induced changes in membrane potential indicates that light-driven pumping increases a dark preexisting potential of about 130 mV only by a small amount (20-30 mV). The complex kinetic features of the membrane potential changes do not closely follow those of the pH changes, indicating that flows of ions other than protons are involved. A qualitative model consistent with the available data is presented. A salient feature of this model is a sudden relaxation of the protonmotive force by a proton inflow through the ATPase when the preexisting protonmotive force is increased by light or respiration and reaches a critical value. The trigger could be either the proton-motive force, the pH gradient, or possibly the internal pH.

Aerobiosis↗

PubMed1976

On the mechanism of action of oligomycin and acidic uncouplers on proton translocation and energy transfer in "sonic" submitochondrial particles.

A study is presented of the effect of acidic uncouplers and oligomycin on energy-linked and passive proton translocation, oxidative phosphorylation, and energy-linked nicotinamide-adenine-nucleotide transhydrogenase in EDTA submitochondrial particles from beef-heart. A flow potentiometric technique has been applied to resolve the kinetics of the initial rapid phase of the redox proton pump. Rapid kinetics analysis shows that carbonyl-cyanide-p-trifluoromethoxyphenyl-hydrazone (FCCP) does not exert any direct effect on redox-linked active proton transport. The uncoupling action of FCCP on oxidative phosphorylation and energy-linked transhydrogenase is shown to be quantitatively accounted for by its promoting effect of passive proton-diffusion across the mitochondrial membrane. Oligomycin depresses passive proton diffusion in EDTA sonic particles and this effect accounts for the coupling action exerted by the antibiotic on oxidative phosphorylation and energy-linked transhydrogenase. In fact, rapid kinetic analysis demonstrates that oligomycin does not directly affect the redox-linked proton pump. The present results show that there does not exist any labile intermediate in the redox-linked proton pump which is sensitive to acidic uncouplers.

Animals↗

PubMed2026

Transcriptomic responses of Porphyrophora sophorae larvae during licorice root colonization reveal coordinated remodeling of translation, mitochondrial energy metabolism and defense-related genes.

BACKGROUND: Porphyrophora sophorae is a subterranean piercing-sucking scale insect that damages licorice (Glycyrrhiza uralensis) roots, but the molecular responses associated with larval root colonization remain insufficiently defined. METHODS: We compared non-parasitic larvae (NP) and root-colonizing larvae (RC) using six RNA-seq libraries, de novo transcriptome assembly, DESeq2-based differential expression analysis, GO/KEGG enrichment, annotation-based candidate gene screening, and RT-qPCR validation of selected genes. RESULTS: Sequencing yielded 260.91 million clean reads, and de novo assembly produced 60,794 non-redundant transcripts. DESeq2 identified 703 FDR-significant DEGs, including 49 upregulated and 654 downregulated genes in RC larvae. Upregulated genes were mainly associated with translation- and ribosome-related processes, whereas downregulated genes were enriched in mitochondrial, oxidation-reduction, energy metabolism, and oxidative phosphorylation-related functions. Annotation-based screening identified 75 FDR-significant candidate genes associated with chemosensation, defense-related responses, and energy metabolism, with mitochondrial energy metabolism-related genes forming the largest module. RT-qPCR validation based on the raw Ct data showed concordant expression directions for ten selected transcript targets. CONCLUSIONS: Root colonization in P. sophorae larvae was associated with coordinated transcriptional remodeling involving selective activation of translation-related processes, adjustment of mitochondrial energy metabolism, and changes in defense-related gene expression. These results provide candidate molecular targets for future functional studies of host contact, feeding establishment, and physiological adjustment in this subterranean scale insect.

Animals↗

PubMed2026

Deletion of neurosecretory proteins GL and GM drives dual anti-obesity effects via appetite suppression and enhanced energy expenditure.

Obesity results from an imbalance between energy intake and expenditure and is regulated by hypothalamic neuropeptide systems. The neurosecretory proteins GL (NPGL) and GM (NPGM) are expressed in the hypothalamus and promote feeding in gain-of-function studies; however, their endogenous physiological roles remain unclear. Here, we show that mice lacking both NPGL and NPGM display a lean phenotype driven by reduced food intake and increased energy expenditure. This anti-obesity phenotype is associated with increased expression of anorexigenic pro-opiomelanocortin in the hypothalamus and enhanced thermogenic activity in brown adipose tissue, marked by elevated uncoupling protein 1. Consistent with these findings, suppression of NPGL/NPGM signaling reduces feeding and alters sympathetic nerve activity. In addition, genome-wide association analysis identifies an obesity-associated variant near the human NPGM locus, suggesting relevance to human energy balance. Together, these findings identify NPGL and NPGM as endogenous regulators of energy homeostasis with potential relevance to obesity.

Animals↗

PubMed1976

Characteristics and energy requirements of an alpha-aminoisobutyric acid transport system in Streptococcus lactis.

Galactose-grown cells of Streptococcus lactis ML3 acculated alpha-aminoisobutyric acid (AIB) by using energy derived from glycolysis and arginine catabolism. The transport system displayed low-affinity Michaelis-Menten saturation kinetics. Using galactose or arginine as energy sources, similar V max and K m values for AIB entry were obtained, but on prolonged incubation the intracellular steady-state concentration of AIB in cells metabolizing arginine was only 65 to 70% that attained by glycolyzing cells. Efflux of AIB FROM PRELOADED CElls was temperature dependent and exhibited the characteristics of a first-order reaction. The rate of AIB exit was accelerated two- to threefold in the presence of metabolizable energy sources. Metabolic inhibitors including p-chloromercuribenzoate, dinitrophenol, azide, arsentate, and N, N'-dicyclohexylcarbodiimide either prevented or greatly reduced AIB uptake. Fluoride, iodoacetate and N-ethylmaleimide abolished galactose-dependent, but not arginine-energized, AIB uptake. K+ and Rb+ reduced the steady-state intracellular AIB concentration by approximately 40%, and these cations also induced rapid efflux of solute from actively transporting cells. Equivalent concentrations (10 mM) of Na+, Li+, or NH4+ were much less inhibitory. The proton-conducting ionophores tetrachlorosalicylanilide and carbonylcyanide m-chlorophenlyhydrazone abolished uptake and induced AIB efflux even though glycolysis and arginine catabolism continued at 60 and 140%, respectively, of control rates. A proton motive force is most likely involved in the active transport of AIB, whereas data from efflux studies suggest that energy is coupled to AIB exit in cells of S. lactis ML3.

Aminoisobutyric Acids↗