Total energy expenditure during total parenteral nutrition: ambulatory patients at home versus patients with sepsis in surgical intensive care

BACKGROUND

To avoid the complications associated with overfeeding or underfeeding, the energy requirements of patients receiving total parenteral nutrition (TPN) must be accurately prescribed. However, until recently it has not been possible to directly measure the rates of total energy expenditure (TEE) in surgical patients receiving TPN.

METHODS

Values for total body water and TEE in four patients with sepsis (mean Acute Physiology and Chronic Health Evaluation [APACHE] score, 10) receiving TPN in surgical intensive care unit and in four patients with chronic intestinal failure receiving long-term TPN at home (HPN) have been determined by using the doubly labeled water technique. The values for TEE have been compared with those of resting energy expenditure obtained with indirect calorimetry (REE CAL) and calculated by using the Harris-Benedict equation (REE HB).

RESULTS

In both the patients with sepsis and the patients receiving HPN the proportion of body weight made up of water was normal for patient age and gender. In patients with sepsis the REE HB significantly (p < 0.05) underestimated the REE CAL (15.39 +/- 3.80 kcal/kg/day-1 versus 31.3 +/- 1.23 kcal/kg/day-1) and was significantly less than the TEE derived by using doubly labeled water (44.62 +/- 1.09 kcal/kg/day-1; p < 0.001). In the ambulatory patients receiving HPN no difference was noted between the REE HB and the REE CAL (18.02 +/- 0.41 kcal/kg/day-1 versus 21.37 +/- 0.94 kcal/kg/day-1). The average TEE for these patients was 30.25 +/- 3.42 kcal/kg/day-1, and this was significantly greater (p < 0.006) than both REE CAL and REE HB:

CONCLUSIONS

This investigation has shown that in patients with sepsis TEE constitutes 1.4 times the REE CAL or approximately 40 kcal/kg/day, whereas in HPN patients TEE can be estimated by supplying 1.4 times the REE or approximately 30 kcal/kg/day-1.

Protonation dynamics of the alpha-toxin ion channel from spectral analysis of pH-dependent current fluctuations

To probe protonation dynamics inside the fully open alpha-toxin ion channel, we measured the pH-dependent fluctuations in its current. In the presence of 1 M NaCl dissolved in H2O and positive applied potentials (from the side of protein addition), the low frequency noise exhibited a single well defined peak between pH 4.5 and 7.5. A simple model in which the current is assumed to change by equal amounts upon the reversible protonation of each of N identical ionizable residues inside the channel describes the data well. These results, and the frequency dependence of the spectral density at higher frequencies, allow us to evaluate the effective pK = 5.5, as well as the rate constants for the reversible protonation reactions: kon = 8 x 10(9) M-1 s-1 and koff = 2.5 x 10(4) s-1. The estimate of kon is only slightly less than the diffusion-limited values measured by others for protonation reactions for free carboxyl or imidazole residues. Substitution of H2O by D2O caused a 3.8-fold decrease in the dissociation rate constant and shifted the pK to 6.0. The decrease in the ionization rate constants caused by H2O/D2O substitution permitted the reliable measurement of the characteristic relaxation time over a wide range of D+ concentrations and voltages. The dependence of the relaxation time on D+ concentration strongly supports the first order reaction model. The voltage dependence of the low frequency spectral density suggests that the protonation dynamics are virtually insensitive to the applied potential while the rate-limiting barriers for NaCl transport are voltage dependent. The number of ionizable residues deduced from experiments in H2O (N = 4.2) and D2O (N = 4.1) is in good agreement.

Solvent effect on phosphatidylcholine headgroup dynamics as revealed by the energetics and dynamics of two gel-state bilayer headgroup structures at subzero temperatures

The packing and dynamics of lipid bilayers at the phosphocholine headgroup region within the temperature range of -40 to -110 degrees C have been investigated by solid-state nuclear magnetic resonance (NMR) measurements of selectively deuterium-labeled H2O/dimyristoylphosphatidylcholine (DMPC) bilayers. Two coexisting signals with 2H NMR quadrupolar, splittings of 36.1 and 9.3 (or smaller) kHz were detected from the -CD3 of choline methyl group. These two signals have been assigned to two coexisting gel-state headgroup structures with fast rotational motion of -CD3 and -N(CD3)3 group, respectively, with a threefold symmetry. The largest quadrupolar splitting of the NMR signal detected from the -CD2 of C alpha and C beta methylene segment was found to be 115.2 kHz, which is 10% lower than its static value of 128.2 kHz. Thus, there are extensive motions of the entire choline group of gel-state phosphatidylcholine bilayers even at a subzero temperature of -110 degrees C. These results strongly support the previous suggestion (E. J. Dufourc, C. Mayer, J. Stohrer, G. Althoff, and G. Kothe, 1992, Biophys. J. 61:42-57) that 31P chemical shift tensor elements of DMPC determined under similar conditions are not the rigid static values. The free energy difference between the two gel-state headgroup structures was determined to be 26.3 +/- 0.9 kJ/mol for fully hydrated bilayers. Furthermore, two structures with similar free energy difference were also detected for "frozen" phosphorylcholine chloride solution in a control experiment, leading to the conclusion that the two structures may be governed solely by the energetics of fully hydrated phosphocholine headgroup. The intermolecular interactions among lipids, however, stabilize the static headgroup structure as evidenced by the apparently lower free energy difference between the two structures for partially hydrated lipid bilayers. Evidence is also presented to suggest that one of the headgroup structures with trimethylammonium group rotation, which is not compatible with the static headgroup structure in crystals, is due to the dielectric relaxation of the slowly reorienting inter bilayer water molecules near the physical edge of membrane surface. Finally, a molecular model of the hydration-induced conformational changes at the torsion angle a5 of the O-C-CN+ bond is proposed to explain the two detected coexisting headgroup structures. These results emphasize the important role of the trimethylammonium group in monitoring the structure and dynamics of the lipid headgroup.

Nutritional assessment with bioelectrical impedance analysis in maintenance hemodialysis patients

Protein energy malnutrition is common among persons with ESRD and contributes substantially to morbidity and mortality. The usual methods of nutritional assessment, such as anthropometry, can be misleading because of altered tissue hydration. Bioelectrical impedance analysis (BIA) has been recommended by some as a practical nutritional assessment tool but has not been validated in patients with ESRD. Thirty-three stable patients on maintenance hemodialysis were evaluated in an ambulatory clinical research center with simultaneous BIA, dual-energy x-ray absorptiometry, and deuterium oxide (D2O) and sodium bromide (NaBr) isotope dilution studies. Standard determinations of total body water (TBW) and body cell mass (BCM) were obtained and compared with values estimated by BIA. Two separate outpatient BIA measurements were also obtained approximately 2 wk before and after the clinical research center evaluation. BCM estimated by BIA was directly correlated (r = 0.92, P < 0.0001) with BCM determined by DEXA and NaBr. TBW estimated by BIA was directly correlated (r = 0.96, P < 0.0001) with TBW determined by deuterium oxide dilution. The reactance to resistance ratio (Xc/R) derived from BIA was inversely correlated (r = -0.73, P < 0.0001) with the extracellular water/TBW ratio determined by NaBr/D2O. Bland-Altman analyses showed that for TBW, BIA was in excellent agreement with D2O dilution. BCM was modestly underestimated by BIA compared with the dual-energy x-ray absorptiometry/NaBr standard and was adjusted by linear regression. The coefficients of variation on repeated BIA measurements were below 4%, demonstrating test-retest reliability. BIA is a valid and reliable method of nutritional assessment in maintenance hemodialysis patients.

Redox-dependent changes in beta-sheet and loop structures of Cu,Zn superoxide dismutase in solution observed by infrared spectroscopy

Redox-dependent conformational changes of bovine Cu,Zn superoxide dismutase in 20 mM phosphate buffer (pH 7.4) were studied at 20 degrees C using Fourier transform infrared spectroscopy. Amide I spectra provide evidence that conformational changes in the protein accompany a change in the oxidation state of copper at the active site. Quantitative analysis of these spectra indicates that both reduced (CuI,ZnII) and oxidized (CuII,ZnII) enzymes are composed of about 35% antiparallel beta-sheet, 45% unordered/loop, and 20% beta-turn structures. Significant redox-dependent changes occur in regions ascribed to beta-sheet and unordered/loop structures that are consistent with an active channel structure wherein the copper ion bonds to imidazolate side chains of His 44, 46, and 118 within the beta-sheet structure and also to the imidazolate side chain of His 61 associated with unordered/loop structure. This study provides the first experimental evidence that an unordered structure can exhibit bands in more than one region, one near 1658 cm-1 and another near 1648 cm-1 in both H2O and D2O solutions. The detected changes in protein conformation are expected to be critical to the catalytic function of this enzyme.

Inositol phosphate capping of the nonreducing termini of lipoarabinomannan from rapidly growing strains of Mycobacterium

Previous studies have demonstrated that the nonreducing termini of the lipoarabinomannan (LAM) from Mycobacterium tuberculosis are extensively capped with mannose residues, whereas those from a fast growing Mycobacterium sp., once thought to be an attenuated strain of M. tuberculosis, are not. The noncapped LAM, termed AraLAM, is known to be more potent than the mannose-capped LAM (ManLAM) in inducing functions associated with macrophage activation. Using a combination of chemical and enzymatic approaches coupled with fast atom bombardment-mass spectrometry analysis, we demonstrated that LAMs from all M. tuberculosis strains examined (Erdman, H37Ra, and H37Rv), as well as the attenuated Mycobacterium bovis BCG strain, are mannose-capped with the extent of capping varying between 40 and 70%. The nonreducing termini of LAM from Mycobacterium leprae were also found to be capped with mannoses but at a significantly lower level. A novel inositol phosphate capping motif was identified on a minor portion of the otherwise uncapped arabinan termini of LAMs from the fast growing Mycobacterium sp. and Mycobacterium smegmatis ATCC 14468 and mc(2)155. In addition, an inositol phosphate tetra-arabinoside was isolated from among endoarabinase digestion products of AraLAM and was shown to induce tumor necrosis factor-alpha production. Accordingly, we concluded that AraLAM is characteristic of some rapidly growing Mycobacterium spp. It is distinct from ManLAMs of M. tuberculosis, M. bovis BCG, and Mycobacterium leprae not only in the absence of mannose-capping but also in containing some terminal inositol phosphate substituents which may account for its particular potency in inducing macrophage activation.

Prediction of body composition of dairy cows at three physiological stages from deuterium oxide and urea dilution

To develop equations for predicting body composition, mature Holstein cows (n = 21) were slaughtered at three physiological stages (-7, 63, and 269 d postpartum) after consecutive intravenous dosing with urea and D2O. Blood was sampled at 0 and 12 min after dosing with urea for determination of urea space and from 0 to 72 h after dosing with D2O. Empty body water and total body water were estimated by dilution kinetics for D2O using two- and one-compartment models, respectively. At slaughter, body components were ground, sampled, and freeze-dried for chemical analysis. Prediction of empty body water by urea space was not an improvement over the prediction by body weight alone. Prediction by D2O dilution explained 73 and 87% of the variation in empty and total body water, respectively. Estimated body protein, as determined from empty body water, predicted actual body protein with an error of 4.7 kg. Daily DMI explained 84% of the variation in the DM of the gastrointestinal tract contents (DM fill). Estimations of empty body fat (R2 = .85) and empty body energy (R2 = .89) from D2O dilution were capable of detecting significant differences in body fat (42.9 kg) and body energy (375 Mcal) across physiological stages and might be useful for prediction of body composition changes during the lactation cycle.

The influence of heavy water on boron requirements for neutron capture therapy

Neutron penetration in tissue is a major limitation of thermal NCT, as such much work has centered upon the epithermal neutron beam in an effort to improve this situation. Further gains in neutron flux penetration, and thus therapeutic ratios, are possible if natural water is replaced with heavy water prior to therapy. Applying MCNP to a heterogeneous ellipsoidal skull/brain model, advantage depth and therapeutic depth parameters are studied as a function of heavy water replacement for a range of tumor to blood boron ratios. Both thermal (0.025 eV) and epithermal (2-7 keV) ideal neutron beams are analyzed. Using 10B ratios in the range of documented human uptake, the thermal advantage depth improved by approximately 0.7 cm for 20% D2O replacement, however, the therapeutic depth increased by less than half this value. For the epithermal beam, both the advantage depth and the therapeutic depth increased by over 1 cm. Effects of heavy water replacement on 10B requirements to therapeutically treat the midline of the brain are also evaluated.

A comparative study of diffusive and osmotic water permeation across bilayers composed of phospholipids with different head groups and fatty acyl chains

Osmotic and diffusive water permeability coefficients Pf and Pd were measured for lipid vesicles of 100-250 nm diameter composed of a variety of phospholipids with different head groups and fatty acyl chains. Two different methods were applied: the H2O/D2O exchange technique for diffusive water flow, and the osmotic technique for water flux driven by an osmotic gradient. For phosphatidylcholines in the liquid-crystalline state at 70 degrees C, permeability constants Pd between 3.0 and 5.2.10(-4) cm/s and ratios Pf/Pd 7 and 23 were observed. The observation of a permeability maximum in the phase transition region and the fact that osmotically driven water flux is higher than diffusive water exchange suggest that water is diffusing through small transient pores arising from density fluctuations in the bilayers. The Pd values depend on the nature of the head group, on the chemical structure of the chains, and on the type of chain linkage. In the case of charged lipids, the ionic strength of the solution has a strong influence. For phosphatidylethanolamines, phosphatidic acids, and ether phosphatidylcholines, permeability constants Pd were considerably lower (2-4.10(-6) cm/s at 70 degrees C). For liquid-crystalline phosphatidylcholines, a strong reduction of Pd after addition of ethanol was observed (2-4.10(-6) cm/s at 70 degrees C). The experimental values are discussed in connection with different permeation models.

Multi-frequency impedance for the prediction of extracellular water and total body water

The relationship between total body water (TBW) and extracellular water (ECW), measured by deuterium oxide dilution and bromide dilution respectively, and impedance and impedance index (height2/impedance) at 1, 5, 50 and 100 kHz was studied. After correction for TBW, ECW was correlated only with the impedance index at 1 and 5 kHz. After correction for ECW, TBW was best correlated with the impedance index at 100 kHz. The correlation of body-water compartments with impedance values obtained with modelling programs was lower than with measured impedance values. Prediction formulas for ECW (at 1 and 5 kHz) and TBW (at 50 and 100 kHz) were developed. The prediction errors for ECW and TBW were 1.0 and 1.7 kg respectively (coefficient of variation 5%). The residuals of both ECW and TBW were related to the ECW/TBW value. Application of the prediction formulas in a population, independently measured, revealed a slight overestimation of TBW and ECW, which could be largely explained by differences in the validation group in body-water distribution and in body build. The ratio of impedance at 1 kHz to impedance at 100 kHz was correlated with body-water distribution (ECW/TBW). The relation is however not strong enough to be useful as a predictor. It is concluded that an independent prediction of ECW and TBW, using impedance at low and high frequency respectively, is possible, but that the bias depends on the body-water distribution and body build of the measured subject.

Fluid changes during pregnancy: use of bioimpedance spectroscopy

The increase in body water during pregnancy is responsible for the largest portion of weight gain and is of interest of clinical practitioners. However, assessing changes in body fluids is not easily accomplished during pregnancy. The purpose of this study was to examine the accuracy of bioelectrical impedance spectroscopy for estimating fluid volumes before, during, and after pregnancy. Ten healthy adult women were recruited for the study. Total body water (TBW) and extracellular fluid (ECF) volume were measured at baseline (preconception); 8-10, 24-26, and 34-36 wk of gestation; and 4-6 wk postpartum by deuterium oxide and NaBr dilution, respectively. Estimates of TBW and ECF were also obtained by bioimpedance spectroscopy (BIS). At baseline, mean values for dilution and BIS estimates of TBW and ECF were 33.2 +/- 4.6 (SD) vs. 31.6 +/- 6.2 liters and 15.2 +/- 1.3 vs. 16.9 +/- 2.3 liters, respectively. TBW and ECF estimated by BIS were not significantly different from the dilution values at any time point. These results suggest that BIS may be useful in estimating volumes of ECF and TBW during pregnancy.

Metabolism of D-[1-3H]glucose, D-[2-3H]glucose, D-[5-3H]glucose, D-[6-3H]glucose and D-[U-14C]glucose by rat and human erythrocytes incubated in the presence of H2O or D2O

The present study investigates whether heavy water affects the efficiency of 3HOH production from D-[1-3H]glucose, D-[2-3H]glucose, D-[5-3H]glucose and D-[6-3H]glucose relative to the total generation of tritiated metabolites produced by either rat or human erythrocytes. The relative 3HOH yield was close to 95% with D-[5-3H]glucose, 72% with D-[2-3H]glucose, 22-32% with D-[1-3H]glucose, and only 12% with D-[6-3H]glucose. In the latter case, the comparison of the specific radioactivity of intracellular and extracellular acidic metabolites, expressed relative to that of 14C-labelled metabolites produced from D-[U-14C]glucose, indicated that the generation of 3HOH from D-[6-3H]glucose occurs at distal metabolic steps, such as the partial reversion of the pyruvate kinase reaction or the interconversion of pyruvate and L-alanine in the reaction catalysed by glutamate-pyruvate transaminase. As a rule, the substitution of H2O by D2O only caused minor to negligible changes in the relative 3HOH yield. This implies that the unexpectedly high deuteration of 13C-labelled D-glucose metabolites recently documented in erythrocytes exposed to D2O cannot be attributed to any major interference of heavy water with factors regulating both the deuteration and detritiation efficiency, such as the enzyme-to-enzyme tunnelling of specific glycolytic intermediates.

Meal frequency influences circulating hormone levels but not lipogenesis rates in humans

To determine whether human lipogenesis is influenced by the frequency of meal consumption, 12 subjects were divided into two groups and fed isocaloric nutritionally adequate liquid diets over 3 days, either as three larger diurnal (n = 6) or as six small, evenly spaced (n = 6) meals per day. On day 2 (08:00 h) of each diet period, 0.7 g deuterium (D) oxide/kg body water was administered and blood was collected every 4 hours over 48 hours for measurement of plasma insulin and glucose-dependent insulinotropic polypeptide (GIP) levels. At each time point, the incorporation of D into plasma triglyceride fatty acid (TG-FA) was also determined by isotope ratio mass spectrometry after TG-FA extraction and combustion/reduction. Insulin and GIP levels were elevated over daytime periods in subjects fed three versus six meals per day. Contribution of de novo synthesis to total TG-FA production was not significantly different for days 2 and 3 in subjects consuming three (6.56% +/- 1.32% and 6.64% +/- 2.08%, respectively) and six (7.67% +/- 2.29% and 7.88% +/- 1.46%, respectively) meals per day. Net TG-FA synthesis rates over days 2 and 3 were 1.47 +/- 0.33 and 1.55 +/- 0.53 g/d, respectively, for subjects fed three meals per day, and 1.64 +/- 0.47 and 1.69 +/- 0.30 g/d for subjects fed six meals per day. These findings suggest that consuming fewer but larger daily meals is not accompanied by increases in TG-FA synthesis, despite the observation of hormonal peaks.

A difference infrared study of hydrogen bonding to the Z. tyrosyl radical of photosystem II

Photosystem II, the photosynthetic water oxidizing complex, contains two well characterized redox active tyrosines, D and Z. D forms a stable radical of unknown function. Z is an electron carrier between the primary chlorophyll donor and the manganese catalytic site. The vibrational difference spectra associated with the oxidation of tyrosines Z and D have been obtained through the use of infrared spectroscopy (MacDonald, G. M., Bixby, K.A., and Barry, B.A. (1993) Proc. Natl. Acad. Sci. U.S.A. 90, 11024-11028). Here, we examine the effect of deuterium exchange on these vibrational difference spectra. While the putative C-O vibration of stable tyrosine radical D. downshifts in 2H2O, the putative C-O vibration of tyrosine radical Z. does not. This result is consistent with the existence of a hydrogen bond to the phenol oxygen of the D. radical; we conclude that a hydrogen bond is not formed to the Z. radical. In an effort to identify the amino acid residue that is the proton acceptor for Z, we have performed global 15N labeling. While significant 15N shifts are observed in the vibrational difference spectrum, substitution of a glutamine for a histidine that is predicted to lie in the environment of tyrosine Z has little or no effect on the difference infrared spectrum. There is also no significant change in the yield or lineshape of the Z. EPR signal under continuous illumination in this mutant. Our results are inconsistent with the possibility that this residue, histidine 190 of the D1 polypeptide, acts as the sole proton acceptor for tyrosine Z.

Role of the carbohydrate moiety of a glucoamylase from Aspergillus awamori var. kawachi in the digestion of raw starch

The digestion of raw starch by a glucoamylase (GA MU-H) from a mutant strain of Aspergillus awamori var. kawachi was closely correlated with mannoside chains O-linked to the Gp-I region (A470-V514), but not sugar chains N-linked to catalytic GAI' domain of GA MU-H. The partial replacement of mannose residues by glucose residues led to a significant decrease raw starch digestion. By the substitution of D2O for H2O in the reaction mixture, the raw starch digestion of GA MU-H decreased to 80% of that at 30 degrees C, although the rate of hydrolysis of soluble starch by and the ability to bind beta-cyclodextrin of GA MU-H were unchanged. Glycerol, known as an antichaotropic reagent, decreased the raw starch digestion of GA MU-H significantly. However, it did not have any effect on the enzymatic activity for soluble starch when soluble starch was the substrate. The efficient digestion of raw starch with raw starch-digesting glucoamylase needed the mannoside chains O-linked to the Gp-I region, which were suggested to contribute to digestion of raw starch through the interaction with water.

Deuterium MR spectroscopy at 4.7 T. Quantification of tumour and subcutaneous tissue blood flow in animal models

Deuterium MR spectroscopy was used for the determination of tissue blood flow (TBF). The tracer D2O was injected into the tissue of interest, and tracer washout was followed using a 4.7 T spectroscopy/imaging unit. Normal subcutaneous tissue in rats was studied, as well as tissue influenced by vasoactive agents (papaverine and adrenaline). The vasoactive agents introduced changes of 40% in TBF, compared with normal tissue. Normal tissue measurements were repeated using various D2O injection volumes (5-400 microliters). The injection volume 5 microliters gave TBF 11.7 +/- 2.0 ml/100 g.min (mean +/- 1 SD). This value was 40% higher than corresponding values observed at larger injection volumes (200-400 microliters). This injection volume effect is probably partly due to a capillary dilution caused by tracer administration, and partly related to the non-physiological deuterium signal decrease observed in dead rats. Blood flow measurements in human colon tumours implanted in nude mice showed a rather poor reproducibility, not improved by the use of a multiple site injection technique.

Effect of vasoactive drugs on tumour blood flow as determined by 2H nuclear magnetic resonance spectroscopy

A selective reduction in tumour blood flow (TBF) could enhance the effects of hyperthermia treatment and of drugs toxic to hypoxic cells. Vasodilator-induced changes in TBF were monitored in transplanted rat fibrosarcomas by non-invasively measuring the uptake of D2O using 2H nuclear magnetic resonance spectroscopy. Hydralazine (1 or 5 mg kg-1) caused a large (45%) reduction in mean arterial blood pressure (MABP) and a 40-60% reduction in TBF. Low-dose hydralazine (0.1 mg kg-1) caused a 20% reduction in MABP but no significant change in TBF. The doses of prazosin (1 mg kg-1) and calcitonin-gene related peptide (CGRP, 1 nmol kg-1) which caused a 20% reduction in MABP led to a 50-60% reduction in TBF. These results demonstrate the advantage of prazosin and CGRP over hydralazine for the reduction of TBF despite a small hypotensive effect. CGRP may be the most suitable of these agents for clinical use because of its short physiological half-life.

Hydrogen background in total body nitrogen estimations

Total body nitrogen (TBN) is measured by in vivo prompt gamma neutron capture analysis. Usually the background under the nitrogen peak is subtracted before calculating TBN from the ratio of nitrogen counts (at 10.8 MeV) to hydrogen counts (at 2.2 MeV). The hydrogen acts as an internal standard. The background under the hydrogen peak is usually ignored. The current study was undertaken to measure the variation of the hydrogen background (HB) in patients of different sizes and to determine whether the accuracy of TBN measurements is improved when an HB correction is incorporated. Heavy-water (D2O) phantoms were used to quantify patient HB. D2O simulates patient neutron scattering without contributing to the hydrogen peak. Equations were developed to predict HB in patient measurements. HB was found to vary from 9% of total counts for a 99 kg subject to 19% for a 7 kg infant. It was demonstrated that the accuracy of TBN measurements is improved for child-sized anthropometric phantoms of known composition when an HB correction is incorporated.

Stability against denaturation mechanisms in halophilic malate dehydrogenase "adapt" to solvent conditions

Malate dehydrogenase from Haloarcula marisomortui (hMDH) is active, soluble and mildly unstable in an unusually wide range of salt conditions and temperatures, making it a particularly interesting model for the study of solvent effects on protein stability. Its denaturation (loss of activity due to concomitant dissociation and unfolding) kinetics was studied as a function of temperature and concentration of NaCl, potassium phosphate or ammonium sulphate in H2O or 2H2O. A transition-state-theory analysis was applied to the data. In all cases, stability (resistance to denaturation) increased with increasing salt concentration, and when 2H2O replaced H2O. Each salt condition was associated with a particular energy regime that dominated stability. In NaCl/H2O, a positive enthalpy term, delta H not equal to 0, always dominated the activation free energy of denaturation, delta G not equal to 0. In potassium phosphate/H2O and ammonium sulphate/H2O, on the other hand, stability was dominated by a negative activation entropy, delta S not equal to 0. and delta H not equal to 0 changed sign between 10 degrees C and 20 degrees C, consistent with a strong hydrophobic effect contribution, in these salting-out solvents. Decreasing stability at low temperatures, favouring cold denaturation, was observed. Replacing H2O by 2H2O strengthened the hydrophobic effect in all conditions. As a consequence, conditions were found in which hMDH was not halophilic; below 10 degrees C, it was stable in approximately 0.1 M NaCl/2H2O. The solution structure and preferential solvent interactions of hMDH in H2O or 2H2O solvents containing NaCl were studied by densimetry and neutron scattering. Despite the different stability of the protein in H2O or 2H2O, an experimentally identical invariant solution particle was formed in both solvents. It had a total volume of 1.165 cm3 g-1 and bound about 0.4 g of H2O (0.44 g of 2H2O) and about 0.08 g NaCl g protein. The impact of these results on a stabilisation model for hMDH, involving ion binding, is discussed.

DNA strand scission and base release photosensitized by metallo-phthalocyanines

Photoirradiation of aqueous solutions of DNA in the presence of Al- or Zn-tetrasulphonated phthalocyanines (AIPcS4 and ZnPcS4) causes formation of strand breaks and liberation of nucleobases. The effect of added D2O, which enhances singlet oxygen (1O2) lifetime, radical scavengers including alcohols and the spin-trap DMPO, as well as superoxide dismutase, indicates that both singlet oxygen (1O2) and free radicals contribute to the production of strand breaks. However, in the case of base release, only free radicals, such as the hydroxyl radical (.OH), appear to be involved in the degradation process. Detection of the characteristic free-radical oxidation products of deoxyribose provides evidence that .OH are involved in the photosensitized DNA damage. EPR and spin trapping data suggest that superoxide (O2.-) is the most likely precursor of .OH and a Fenton-type mechanism is proposed for their formation.

DNA binding to crystalline silica characterized by Fourier-transform infrared spectroscopy

The interaction of DNA with crystalline silica in buffered aqueous solutions at physiologic pH has been investigated by Fourier-transform infrared spectroscopy (FT-IR). In aqueous buffer, significant changes occur in the spectra of DNA and silica upon coincubation, suggesting that a DNA-silica complex forms as silica interacts with DNA. As compared to the spectrum of silica alone, the changes in the FT-IR spectrum of silica in the DNA-silica complex are consistent with an Si-O bond perturbation on the surface of the silica crystal. DNA remains in a B-form conformation in the DNA-silica complex. The most prominent changes in the DNA spectrum occur in the 1225 to 1000 cm-1 region. Upon binding, the PO2- asymmetric stretch at 1225 cm-1 is increased in intensity and slightly shifted to lower frequencies; the PO2- symmetric stretch at 1086 cm-1 is markedly increased in intensity and the band at 1053 cm-1, representing either the phosphodiester or the C-O stretch of DNA backbone, is significantly reduced in intensity. In D2O buffer, the DNA spectrum reveals a marked increase in intensity of the peak at 1086 cm-1 and a progressive decrease in intensity of the peak at 1053 cm-1 when DNA is exposed to increasing concentrations of silica. The carbonyl band at 1688 cm-1 diminishes and shifts to slightly lower frequencies with increasing concentrations of silica. The present study demonstrates that crystalline silica binds to the phosphate-sugar backbone of DNA.(ABSTRACT TRUNCATED AT 250 WORDS)

A new method for proton detection of H2(17)O with potential applications for functional MRI

A method is presented for the sensitive detection of minute amounts of H2(17)O. The method is based on the increase of the T2 of the water protons following an irradiation of the 17O resonance frequency, due to the partial or full decoupling of the 1H-17O spin-spin interaction. It is demonstrated that when 17O concentrations are low, full decoupling is achieved, and at short echo times the increase in the amplitude of the proton echo signal is proportional to the 17O content of the sample. The potential of the method for indirect 17O imaging is substantiated by a simple one dimensional projection of cylindrical phantoms containing various 17O concentrations. Using interleaved sequences with and without 17O decoupling, errors due to time dependent effects are minimized.

Mechanism of interaction between actin and membrane lipids: a pressure-tuning infrared spectroscopy study

Using pressure-tuning Fourier transform infrared spectroscopy to study an in vitro system consisting of actin and distearoyl-phosphatidylcholine (DSPC) liposomes, we have determined the mechanism of interaction between actin and membrane lipids. This interaction results in a significant conformational change in actin molecules. Analysis of the amide I band of actin shows an increase in the beta-sheets to alpha-helix ratio, in random turns, and in interactions between actin monomers. In the absence of lipids, the actin molecules are denatured by pressures of 8 x 10(8) Pa and more, which give rise to a random organization of the peptide chain. However, in the presence of DSPC liposomes, pressure greater than 2 x 10(8) Pa induces a change in actin conformation, which is dominated by strongly interacting beta-sheets. As the spectra of the lipid molecules are not changed by the presence of actin, the organization of the lipid molecules in the bilayer is not affected by the protein. It is concluded from these results that this interaction of actin with membrane lipids involves very few lipid molecules. These lipid molecules may interact with actin at a few specific sites on the protein.