Is there an energy conservation “system” in brain that protects against the consequences of energy depletion?

A poorly understood marked decrease (circa 50% of control) in local cerebral glucose utilization is caused by sublethal doses of NaCN. The decrease is global, occurring in essentially all brain regions and is entirely reversible within hours, leaving no obvious pathology. This event is not unique to NaCN in so far as a strikingly similar pattern of decreased glucose utilization occus with some other toxins. Nor can it be attributed to a direct action of NaCN since local application by microdialysis to the striatum produces a global depression. These results imply that some widely distributed system or substance is involved. We speculate the existence of a system possibly related to the reticular activating system that senses a fall in energy production and acts globally to make cells quiescent and thus would give some protection from excitotoxic driven damage.Special issue dedicated to Dr. Sidney Ochs.     

Evaluation of the effects of cosmetic or dermo-pharmaceutical products on cutaneous energy metabolism using the Episkin model of reconstructed epidermis

This study was implemented to test the Episkin model of reconstructed epidermis in the evaluation of the efficacy of cosmetic or dermopharmaceutical products on cutaneous energy metabolism. The energy metabolism is evaluated by measuring the concentration of intracellular ATP by a method using an ultrasensitive bioluminescent reaction. The work presented compares results obtained in reconstructed epithelium and monolayer primary cultures of human keratinocytes.After application of a hydrosoluble product, the increase in intracellular ATP is identical in a monolayer culture of keratinocytes (+239±18% versus control) and in Episkin (+248±21% versus control). An emulsion was also tested on the two models. It is only possible to test the emulsion at a dilution of under 0.05% on a keratinocyte culture, and this means that the real efficacy of the product is underestimated (+145±18% versus control). The three-dimensional model enables the application of the undiluted emulsion, and the results show an increase in intracellular ATP of +420±80% versus control: products in final formulation can be tested in normal conditions of use.Abbreviations BPE bovine pituitary extract - DMEM Dulbecco's modified Eagle's medium - EDTA ethylene diamine tetraacetic acid - EGF epidermal growth factor - K-SFM keratinocytes serum free medium - MTT 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide - O/W oil in water - PBS phosphate-buffered saline     

Energy minimization method using automata network for sequence and side-chain conformation prediction from given backbone geometry

Globular proteins have high packing densities as a result of residue side chains in the core achieving a tight, complementary packing. The internal packing is considered the main determinant of native protein structure. From that point of view, we present here a method of energy minimization using an automata network to predict a set of amino acid sequences and their side-chain conformations from a desired backbone geometry for de novo design of proteins. Using discrete side-chain conformations, that is, rotamers, the sequence generation problem from a given backbone geometry becomes one of combinatorial problems. We focused on the residues composing the interior core region and predicted a set of amino acid Sequences and their side-chain conformations only from a given backbone geometry. The kinds of residues were restricted to six hydrophobic amino acids (Ala, Ile, Met, Leu, Phe, and Val) because the core regions are almost always composed of hydrophobic residues. The obtained sequences were well packed as was the native sequence. The method can be used for automated sequence generation in the de novo design of proteins. © 1994 Wiley-Liss, Inc.     

Intrinsic pKas of ionizable residues in proteins: An explicit solvent calculation for lysozyme

Molecular dynamics simulations of triclinic hen egg white lysozyme in aqueous solution were performed to calculate the intrinsic pK_as of 14 ionizable residues. An all-atom model was used for both solvent and solute, and a single 180 ps simulation in conjunction with a Gaussian fluctuation analysis method was used. An advantage of the Gaussian fluctuation method is that it only requires a single simulation of the system in a reference state to calculate all the pK_as in the protein, in contrast to multiple simulations for the free energy perturbation method. pK_int shifts with respect to reference titratable residues were evaluated and compared to results obtained using a finite difference Poisson-Boltzmann (FDPB) method with a continuum solvent model; overall agreement with the direction of the shifts was generally observed, though the magnitude of the shifts was typically larger with the explicit solvent model. The contribution of the first solvation shell to the total charging free energies of the titratable groups was explicitly evaluated and found to be significant. Dielectric shielding between pairs of titratable groups was examined and found to be smaller than expected. The effect of the approximations used to treat the long-range interactions on the pK_int shifts is discussed. © 1994 Wiley-Liss, Inc.     

Enantiomerization of 2,2′-diisopropylbiphenyl during chiral inclusion gas chromatography: Determination of the rotational energy barrier by computer simulation of dynamic chromatographic elution profiles

By computer simulation of experimental dynamic gas chromatographic elution profiles, the rotational energy barrier ΔG⁼ of racemic 2,2′-diisopropylbiphenyl has been determined as 114.6–115.0 kJ/mol (75–100°C). These data are in good agreement with a value that was determined previously by measuring the racemization kinetics of an enriched sample. This indicates that there is no measurable catalytic or inhibitory effect of the stationary phase. © 1994 Wiley-Liss, Inc.     

The sequence of electron carriers in the reaction of cytochromec oxidase with oxygen

Kinetic studies of the electron transfer processes performed by cytochrome oxidase have assigned rates of electron transfer between the metal centers involved in the oxidation of ferrocytochromec by molecular oxygen. Transient-state studies of the reaction with oxygen have led to the proposal of a sequence of carriers from cytochromec, to Cu_A, to cytochromea, and then to the binuclear (i.e., cytochromea ₃-Cu_B) center. Electron exchange rates between these centers agree with relative center-to-center distances as follows; cytochromec to Cu_A 5–7 Å, cytochromec to cytochromea 20–25 Å, Cu_A to cytochromea 14–16 Å and cytochromea to cytochrome a₃-Cu_B 8–10 Å. It is proposed that the step from cytochromea to the binuclear center is the key control point in the reaction and that this step is one of the major points of energy transduction in the reaction cycle.     

The Response to Exercise with Constant Energy Intake in Identical Twins

Seven pairs of young adult male identical twins completed a negative energy balance protocol during which they exercised on cycle ergometers twice a day, 9 out of 10 days, over a period of 93 days while being kept on a constant daily energy and nutrient intake. The total energy deficit caused by exercise above the estimated energy cost of body weight maintenance reached 244 ± 9.8 MJ (Mean ± SEM). Baseline energy intake was estimated over a period of 17 days preceding the negative energy balance protocol. Mean body weight loss was 5.0 kg (SEM = 0.6) (p <0.001) and it was entirely accounted for by the loss of fat mass (p <0.001). Fat-free mass was unchanged. Body energy losses reached 191 MJ (SEM = 24) (p <0.001) which represented about 78% of the estimated energy deficit. Subcutaneous fat loss was slightly more pronounced on the trunk than on the limbs as estimated from skinfolds, circumferences, and computed tomography (CT). The reduction in CT-assessed abdominal visceral fat was quite striking, from 81 cm² (SEM = 5) to 52 cm² (SEM = 6) (p <0.001). At the same submaximal power output level, subjects oxidized more lipids than carbohydrates after the program as indicated by the changes in the respiratory exchange ratio (p <0.05). Intrapair resemblance was observed for the changes in body weight (p <0.05), fat mass (P <0.01), percent fat (p <0.01), body energy content (p <0.01), sum of 10 skinfolds (p <0.01), abdominal visceral fat (p <0.01), fasting plasma triglycerides (p <0.05) and cholesterol (p <0.05), maximal oxygen uptake (p <0.05), and respiratory exchange ratio during submaximal work (p <0.01). We conclude that even though there were large individual differences in response to the negative energy balance and exercise protocol, subjects with the same genotype were more alike in responses than subjects with different genotypes particularly for body fat, body energy, and abdominal visceral fat changes. High lipid oxidizers and low lipid oxidizers during sub-maximal exercise were also seen despite the fact that all subjects had experienced the same exercise and nutritional conditions for about three months.     

PHYSIOLOGICAL ACCLIMATION OF MARINE PHYTOPLANKTON TO DIFFERENT NITROGEN SOURCES1

We examined the energetic dependency of the biochemical and physiological responses of Thalassiosira pseudonana Hasle and Heimdal. Chaetoceros gracilis Schütt, Dunaliella tertiolecta Butcher, and Gymnodinium sanguineum Hirasaka to NH₄⁺, NO₃^?, and urea by growing them at subsaturating and saturating photon flux (PF). At subsaturating PF, when energy was limiting, NO₃^? and NH₄⁺ grown cells had similar growth rates and C and X quotas. Therefore, NO₃^? grown cells used up to 48% more energy than NH₄⁺ grown cells to assimilate carbon and nitrogen. Based on our measurements of pigments, chlorophyll-a-specific in vivo absorption cross-section, and fluorescence-chlorophyll a^?1, we suggest that NO₃^?, grown cells do not compensate for the greater energy requirements of NO₃^? reduction by trapping more light energy. At saturating PF, when energy is not limiting, the utilization of NO₃^?, compared to NH₄⁺ resulted in lower growth rates and N quotas in Thalassiosira pseudonana and lower N quotas in Chaetoceros gracilis, suggesting enzymatic rather than energetic limitations to growth. The utilization of urea compared to Nh₄⁺ resulted in lower growth rates in Chaetoceros gracilis and Gymnodinium sanguineum (saturating PF) and in lower N quotas in all species tested at both subsaturating and saturating PF. The high C:N ratios observed in all urea-grown species suggest that nitrogen assimilation may be limited by urea uptake or deamination and that symptoms of N limitation in microalgae may be induced by the nature of the N source in addition to the N supply rate. Our results provide new eridence that the maximum growth rates of microalgae may be limited by enzymatic processes associated with the assimilation of NO₃^?, or urea.     

Gravimetricvs. respirometric determination of metabolic efficiency in caterpillars ofPieris brassicae

Conventional gravimetry and a combination of gravimetry and respirometry were compared for their precision in measuring respiration and metabolic efficiency of growth of final stadiumPieris brassicae L. (Pieridae, Lepidoptera) caterpillars. This was done both for caterpillars feeding on an artificial diet and for caterpillars feeding on excised leaf material of a host plant,Brassica oleracea L. Gravimetry produced significantly greater variation in the total amount of matter respired and the metabolic efficiency than indirect calorimetry for caterpillars feeding on plant material, while the two methods gave similar results for the caterpillars reared on a meridic artificial diet. Respirometry (indirect calorimetry) revealed that caterpillars feeding on the artificial diet were growing with a higher metabolic efficiency than caterpillars feeding on the host plant. This difference was not revealed by conventional gravimetry. It is argued that metabolic efficiencies as derived from gravimetric budget calculations are subject to a number of random errors that distort precise determination of metabolic efficiencies in studies involving plant food.     

Individual amino acid balances in young lean and obese Zucker rats fed a cafeteria diet

The amino acid composition of the diet ingested by reference and cafeteria diet-fed lean and obese Zucker rats has been analyzed from day 30 to 60 after birth. Their body protein amino acid composition was measured, as well as the urinary and faecal losses incurred during the period studied. The protein actually selected by the rats fed the cafeteria diet had essentially the same amino acid composition as the reference diet. The mean protein amino acid composition of the rat showed only small changes with breed, age or diet.Cafeteria-fed rats had a higher dietary protein digestion/absorption efficiency than reference diet-fed rats. Obese rats wasted a high proportion of dietary amino acids when given the reference diet, but not on the cafeteria diet. In all cases, the amino acids lost as such in the urine were a minimal portion of available amino acids.In addition to breed, the rates of protein accretion are deeply influenced by diet, but even more by the age — or size — of the animals: cafeteria-fed rats grew faster, to higher body protein settings, but later protein accrual decreased considerably; this is probably due to a limitation in the blueprint for growth which restricts net protein deposition when a certain body size is attained. Obese rats, however, kept accuring protein with high rates throughout.Diet composition — and not protein availability or quality-induced deep changes in amino acid metabolism. Since the differences in the absolute levels of dietary protein or carbohydrate energy ingested by rats fed the reference or cafeteria diets were small, it can be assumed that high (lipid) energy elicits the changes observed in amino acid metabolism by the cafeteria diet. The effects induced in the fate of the nitrogen ingested were more related to the fractional protein energy proportion than to its absolute values. Cafeteria-fed rats tended to absorb more amino acids and preserve them more efficiently; these effects were shown even under conditions of genetic obesity.There were deep differences in handling of dietary amino acids by dietary or genetically obese rats. The former manage to extract and accrue larger proportions of their dietary amino acids than the latter. The effects of both models of amino acid management were largely additive, suggesting that the mechanisms underlying the development of obesity did not run in parallel to those affecting the control of amino acid utilization. Obesity may be developed in both cases despite a completely different strategy of amino acid assimilation, accrual and utilization. (Mol Cell Biochem121: 45–58, 1993)