Science in the Public Mind: sources and consequences of antipathy.

Public attitudes toward science in the United States can profoundly affect national well-being, and even national security. We live in a time when these attitudes are considerably more negative than usual. This critical assessment identifies a number of contributors to public antipathy toward science, some of which are intrinsic to the nature of science and as old as science itself, and some of which are external to science, have arisen recently, and may be unique to the present. Historic examples of scientific developments and challenges and two major current examples (the COVID-19 pandemic and anthropogenic climate change) illustrate the interplay of science and public attitudes and actions, and the development and consequences of antipathy toward science. The problem areas that contribute to public antipathy in turn suggest strategies that may mitigate the antipathy, although some social and political factors will impose limits on possible mitigation. The energy required to sustain an acceptable level of civilization needs to be acknowledged, along with the need to minimize anthropogenic climate change.

The pathway of O2to the active site in heme-copper oxidases.

The route of O2to and from the high-spin heme in heme-copper oxidases has generally been believed to emulate that of carbon monoxide (CO). Time-resolved and stationary infrared experiments in our laboratories of the fully reduced CO-bound enzymes, as well as transient optical absorption saturation kinetics studies as a function of CO pressure, have provided strong support for CO binding to CuB⁺ on the pathway to and from the high-spin heme. The presence of CO on CuB⁺ suggests that O2binding may be compromised in CO flow-flash experiments. Time-resolved optical absorption studies show that the rate of O2and NO binding in the bovine enzyme (1 × 108M⁻¹s⁻¹) is unaffected by the presence of CO, which is consistent with the rapid dissociation (t½ = 1.5µs) of CO from CuB⁺. In contrast, in Thermus thermophilus (Tt) cytochrome ba3 the O2and NO binding to heme a3 slows by an order of magnitude in the presence of CO (from 1 × 109 to 1 × 108M⁻¹s⁻¹), but is still considerably faster (~10µs at 1atm O2) than the CO off-rate from CuB in the absence of O2(milliseconds). These results show that traditional CO flow-flash experiments do not give accurate results for the physiological binding of O2and NO in Tt ba3, namely, in the absence of CO. They also raise the question whether in CO flow-flash experiments on Tt ba3 the presence of CO on CuB⁺ impedes the binding of O2to CuB⁺ or, if O2does not bind to CuB⁺ prior to heme a3, whether the CuB⁺-CO complex sterically restricts access of O2to the heme. Both possibilities are discussed, and we argue that O2binds directly to heme a3 in Tt ba3, causing CO to dissociate from CuB⁺ in a concerted manner through steric and/or electronic effects. This would allow CuB⁺ to function as an electron donor during the fast (5µs) breaking of the OO bond. These results suggest that the binding of CO to CuB⁺ on the path to and from heme a3 may not be applicable to O2and NO in all heme-copper oxidases. This article is part of a Special Issue entitled: Vibrational spectroscopies and bioenergetic systems.

Nature of bonding in complexes containing "supershort" metal-metal bonds. raman and theoretical study of M2(dmp)4 [M = Cr (natural abundance Cr, 50Cr, and 54Cr) and Mo; dmp = 2,6-dimethoxyphenyl].

We report an investigation of complexes of the type M(2)(dmp)(4) (M = Mo, Cr; dmp = 2,6-dimethoxyphenyl) using resonance Raman (RR) spectroscopy, Cr isotopic substitution, and density functional theory (DFT) calculations. Assignment of the Mo-Mo stretching vibration in the Mo(2) species is straightforward, as evidenced by a single resonance-enhanced band at 424 cm(-1), consistent with an essentially unmixed metal-metal stretch, and overtones of this vibration. On the other hand, the Cr(2) congener has no obvious metal-metal stretching mode near 650-700 cm(-1), where empirical predictions based on the Cr-Cr distance as well as DFT calculations suggest that this vibration should appear if unmixed. Instead, three bands are observed at 345, 363, and 387 cm(-1) that (a) have relative RR intensities that are sensitive to the Raman excitation frequency, (b) exhibit overtones and combinations in the RR spectra, and (c) shift in frequency upon isotopic substitution ((50)Cr and (54)Cr). DFT calculations are used to model the vibrational data for the Mo(2) and Cr(2) systems. Both the DFT results and empirical predictions are in good agreement with experimental observations in the Mo(2) complex, but both, while mutually consistent, differ radically from experiment in the Cr(2) complex. Our experimental and theoretical results, especially the Cr isotope shifts, clearly demonstrate that the potential energy of the Cr-Cr stretching coordinate is distributed among several normal modes having both Cr-Cr and Cr-ligand character. The general significance of these results in interpreting spectroscopic observations in terms of the nature of metal-metal multiple bonding is discussed.

Energy uptake and allocation during ontogeny.

All organisms face the problem of how to fuel ontogenetic growth. We present a model, empirically grounded in data from birds and mammals, that correctly predicts how growing animals allocate food energy between synthesis of new biomass and maintenance of existing biomass. Previous energy budget models have typically had their bases in rates of either food consumption or metabolic energy expenditure. Our model provides a framework that reconciles these two approaches and highlights the fundamental principles that determine rates of food assimilation and rates of energy allocation to maintenance, biosynthesis, activity, and storage. The model predicts that growth and assimilation rates for all animals should cluster closely around two universal curves. Data for mammals and birds of diverse body sizes and taxa support these predictions.

Revisiting a model of ontogenetic growth: estimating model parameters from theory and data.

The ontogenetic growth model (OGM) of West et al. provides a general description of how metabolic energy is allocated between production of new biomass and maintenance of existing biomass during ontogeny. Here, we reexamine the OGM, make some minor modifications and corrections, and further evaluate its ability to account for empirical variation on rates of metabolism and biomass in vertebrates both during ontogeny and across species of varying adult body size. We show that the updated version of the model is internally consistent and is consistent with other predictions of metabolic scaling theory and empirical data. The OGM predicts not only the near universal sigmoidal form of growth curves but also the M(1/4) scaling of the characteristic times of ontogenetic stages in addition to the curvilinear decline in growth efficiency described by Brody. Additionally, the OGM relates the M(3/4) scaling across adults of different species to the scaling of metabolic rate across ontogeny within species. In providing a simple, quantitative description of how energy is allocated to growth, the OGM calls attention to unexplained variation, unanswered questions, and opportunities for future research.

Scaling of number, size, and metabolic rate of cells with body size in mammals.

The size and metabolic rate of cells affect processes from the molecular to the organismal level. We present a quantitative, theoretical framework for studying relationships among cell volume, cellular metabolic rate, body size, and whole-organism metabolic rate that helps reveal the feedback between these levels of organization. We use this framework to show that average cell volume and average cellular metabolic rate cannot both remain constant with changes in body size because of the well known body-size dependence of whole-organism metabolic rate. Based on empirical data compiled for 18 cell types in mammals, we find that many cell types, including erythrocytes, hepatocytes, fibroblasts, and epithelial cells, follow a strategy in which cellular metabolic rate is body size dependent and cell volume is body size invariant. We suggest that this scaling holds for all quickly dividing cells, and conversely, that slowly dividing cells are expected to follow a strategy in which cell volume is body size dependent and cellular metabolic rate is roughly invariant with body size. Data for slowly dividing neurons and adipocytes show that cell volume does indeed scale with body size. From these results, we argue that the particular strategy followed depends on the structural and functional properties of the cell type. We also discuss consequences of these two strategies for cell number and capillary densities. Our results and conceptual framework emphasize fundamental constraints that link the structure and function of cells to that of whole organisms.

The metabolic basis of whole-organism RNA and phosphorus content.

Understanding the storage, flux, and turnover of nutrients in organisms is important for quantifying contributions of biota to biogeochemical cycles. Here we present a model that predicts the storage of phosphorus-rich RNA and whole-body phosphorus content in eukaryotes based on the mass- and temperature-dependence of ATP production in mitochondria. Data from a broad assortment of eukaryotes support the model's two main predictions. First, whole-body RNA concentration is proportional to mitochondrial density and consequently scales with body mass to the -1/4 power. Second, whole-body phosphorus content declines with increasing body mass in eukaryotic unicells but approaches a relatively constant value in large multicellular animals because the fraction of phosphorus in RNA decreases relative to the fraction in other pools. Extension of the model shows that differences in the flux of RNA-associated phosphorus are due to the size dependencies of metabolic rate and RNA concentration. Thus, the model explicitly links two biological currencies at the individual level: energy in the form of ATP and materials in the form of phosphorus, both of which are critical to the functioning of ecosystems. The model provides a framework for linking attributes of individuals to the storage and flux of phosphorus in ecosystems.

Fast photoreduction of a heme peptide encapsulated in nanostructured materials.

Microperoxidase-11 has been immobilized on siliceous materials MCM-41 and SBA-15 and on amino-functionalized SBA-15. Resonance Raman spectroscopy has provided solid evidence that the exogenous species occupy the pores of the mesoporous silica materials. Photoreduction of the microperoxidase-11 Fe(III) center has been observed to occur in the immobilized samples and results in a long-lived stable reduced heme. Reoxidation of the heme occurs upon addition of oxygen, and the redox cycle can be repeated numerous times. The source of the electron resulting in reduction of the heme is proposed to originate from the silica matrix, and functionalization of silica surface is suggested to facilitate electron transfer to the heme.

FTIR studies of internal proton transfer reactions linked to inter-heme electron transfer in bovine cytochrome c oxidase.

FTIR difference spectroscopy is used to reveal changes in the internal structure and amino acid protonation states of bovine cytochrome c oxidase (CcO) that occur upon photolysis of the CO adduct of the two-electron reduced (mixed valence, MV) and four-electron reduced (fully reduced, FR) forms of the enzyme. FTIR difference spectra were obtained in D(2)O (pH 6-9.3) between the MV-CO adduct (heme a(3) and Cu(B) reduced; heme a and Cu(A) oxidized) and a photostationary state in which the MV-CO enzyme is photodissociated under constant illumination. In the photostationary state, part of the enzyme population has heme a(3) oxidized and heme a reduced. In MV-CO, the frequency of the stretch mode of CO bound to ferrous heme a(3) decreases from 1965.3 cm(-1) at pH*

An EPR, ESEEM, structural NMR, and DFT study of a synthetic model for the covalently ring-linked tyrosine-histidine structure in the heme-copper oxidases.

We report CW-EPR, ESEEM, and structural NMR results, as well as DFT calculations, on model compounds relevant to the unusual cross-linked Tyr-His (YH) moiety at the active site of the heme-copper oxidases. CW-EPR spectra of an (15)N isotopically labeled 4-methyl-2-(4-methyl-imidazole-1-yl)-phenol radical are nearly identical to those of the natural abundance (14)N compound. We obtain good simulations of these EPR spectra without including hyperfine couplings to the nitrogen nuclei. This implies that the electron distribution of the radical is largely localized on the phenol ring with only a small amount of spin delocalized onto the nitrogens of the imidazole. Using three-pulse ESEEM spectroscopy, we have successfully detected the two imidazole ring nitrogens, one near the "exact cancellation" ESEEM condition and the other more weakly coupled. We assign these to the imino and amino nitrogens, respectively, based on DFT calculations performed on this radical species. The experimental results and the supporting density functional calculations clearly show that the imidazole substituent has only a minor effect on the electronic structure of the substituted phenol radical.

Direct infrared detection of the covalently ring linked His-Tyr structure in the active site of the heme-copper oxidases.

Infrared spectroscopy, isotopic labeling ([(15)N(delta,epsilon)]histidine and ring-deuterated tyrosine), synthetic model studies, and normal mode calculations are employed to search for the spectroscopic signatures of the unique, covalently linked (His N(epsilon)-C(epsilon) Tyr) biring structure in the heme-copper oxidases. The specific enzyme examined is the cytochrome bo(3) quinol oxidase of E. coli. Infrared features of histidine and tyrosine are identified in the frequency regions of imidazole and phenol ring stretching modes (1350-1650 cm(-1)) and C-H and N-H stretching modes as well as overtones and combinations (>3000 cm(-1)). Two of these, at ca. 1480 and 1550 cm(-1), and their combination tones between 3010 and 3040 cm(-1), are definitively identified with the biring structure involving H284 and Y288 in the E. coli enzyme. Studies of a synthetic analogue of the H-Y structure, 4-methylimidazole covalently linked to p-cresol, show that a feature near 1540 cm(-1) is unique to the biring structure and is absent from the infrared spectrum of 4-methylimidazole or p-cresol alone. This feature is readily detectable by infrared difference techniques, and offers a direct spectroscopic probe for potential radical production involving the H-Y structure in the O(2) reduction cycle of the oxidases.

Allometric scaling of metabolic rate from molecules and mitochondria to cells and mammals.

The fact that metabolic rate scales as the three-quarter power of body mass (M) in unicellular, as well as multicellular, organisms suggests that the same principles of biological design operate at multiple levels of organization. We use the framework of a general model of fractal-like distribution networks together with data on energy transformation in mammals to analyze and predict allometric scaling of aerobic metabolism over a remarkable 27 orders of magnitude in mass encompassing four levels of organization: individual organisms, single cells, intact mitochondria, and enzyme molecules. We show that, whereas rates of cellular metabolism in vivo scale as M(-1/4), rates for cells in culture converge to a single predicted value for all mammals regardless of size. Furthermore, a single three-quarter power allometric scaling law characterizes the basal metabolic rates of isolated mammalian cells, mitochondria, and molecules of the respiratory complex; this overlaps with and is indistinguishable from the scaling relationship for unicellular organisms. This observation suggests that aerobic energy transformation at all levels of biological organization is limited by the transport of materials through hierarchical fractal-like networks with the properties specified by the model. We show how the mass of the smallest mammal can be calculated (approximately 1 g), and the observed numbers and densities of mitochondria and respiratory complexes in mammalian cells can be understood. Extending theoretical and empirical analyses of scaling to suborganismal levels potentially has important implications for cellular structure and function as well as for the metabolic basis of aging.

Time-resolved step-scan Fourier transform infrared spectroscopy of the CO adducts of bovine cytochrome c oxidase and of cytochrome bo(3) from Escherichia coli.

We have used cryogenic difference FTIR and time-resolved step-scan Fourier transform infrared (TR-FTIR) spectroscopies to explore the redox-linked proton-pumping mechanism of heme-copper respiratory oxidases. These techniques are used to probe the structure and dynamics of the heme a(3)-Cu(B) binuclear center and the coupled protein structures in response to the photodissociation of CO from heme Fe and its subsequent binding to and dissociation from Cu(B). Previous cryogenic (80 K) FTIR CO photodissociation difference results were obtained for cytochrome bo(3), the ubiquinol oxidase of Escherichia coli [Puustinen, A., et al. (1997) Biochemistry 36, 13195-13200]. These data revealed a connectivity between Cu(B) and glutamic acid E286, a residue which has been implicated in proton pumping. In the current work, the same phenomenon is observed using the CO adduct of bovine cytochrome aa(3) under cryogenic conditions, showing a perturbation of the equivalent residue (E242) to that in bo(3). Furthermore, using time-resolved (5 micros resolution) step-scan FTIR spectroscopy at room temperature, we observe the same spectroscopic perturbation in both cytochromes aa(3) and bo(3). In addition, we observe evidence for perturbation of a second carboxylic acid side chain, at higher frequency in both enzymes at room temperature. The high-frequency feature does not appear in the cryogenic difference spectra, indicating that the perturbation is an activated process. We postulate that the high-frequency IR feature is due to the perturbation of E62 (E89 in bo(3)), a residue near the opening of the proton K-channel and required for enzyme function. The implications of these results with respect to the proton-pumping mechanism are discussed. Finally, a fast loss of over 60% of the Cu(B)-CO signal in bo(3) is observed and ascribed to one or more additional conformations of the enzyme. This fast conformer is proposed to account for the uninhibited reaction with O(2) in flow-flash experiments.

Resonance Raman, X-ray Crystallographic, and Magnetic Susceptibility Studies of Metal-Metal-Bonded MoRu and WOs Porphyrin Dimers. 1. Evidence for an Unusual MO Diagram.

Solution (VT NMR, Evans method magnetic susceptibility, resonance Raman) and solid-state (SQUID magnetic susceptibility, X-ray crystallography) spectroscopic studies of intertriad heterodimeric [(OEP)MoRu(OEP)] (1), [(OEP)WOs(OEP)] (2), and [(OEP)MoRu(TPP)]PF(6) (3(+)) metalloporphyrins are reported (OEP = 2,3,7,8,12,13,17,18-octaethylporphyrinato; TPP = 5,10,15,20-tetraphenylporphyrinato). Solution and solid-state magnetic susceptibility data indicate that 1 and 2 contain two unpaired electrons in the ground electronic configuration. The presence of a delta bond in 3(+) has been confirmed by structural characterization. The experimental evidence is consistent with a molecular orbital ordering, sigma < pi < delta < pi < delta, which is different from that seen for homologous metalloporphyrin dimers with homometallic or intratriad heterometallic multiple metal-metal bonds. Resonance Raman data suggest that the heterometallic bonds are slightly stronger than isoelectronic homometallic species.

Resonance Raman and X-ray Crystallographic Studies of Intertriad Metal-Metal Bonds. 2. WRu and MoOs Porphyrin Dimers.

Solution ((1)H NMR, Evans method magnetic susceptibility, resonance Raman) and X-ray crystallographic spectroscopic studies of intertriad heterodimeric [(OEP)MoOs(OEP)] (3), [(OEP)WRu(OEP)] (4), [(OEP)MoOs(TPP)]PF(6) (5(+)), and [(OEP)WRu(TPP)]PF(6) (6(+)) metalloporphyrins are reported (OEP = 2,3,7,8,12,13,17,18-octaethylporphyrinato; TPP = 5,10,15,20-tetraphenylporphyrinato). Evans method magnetic susceptibility data indicate that 3 and 4 contain two unpaired electrons in the ground electronic configuration. Resonance Raman spectra of 3, 4, 5(+), and 6(+) suggest that WRu bonds are 5-10% stronger than corresponding MoOs species. Structural characterization of 5(+) and 6(+) demonstrates metal-metal bond lengths of 2.30 (WRu) and 2.24 (MoOs) Å, respectively. The possibility of a special stability associated with polar heterometallic multiple bonds is discussed.

Resonance Raman Spectra of [M(6)X(8)Y(6)](2)(-) Cluster Complexes (M = Mo, W; X, Y = Cl, Br, I).

Resonance Raman spectra of the cubic metal-halide complexes having the general formula [M(6)X(8)Y(6)](2)(-) (M = Mo or W; X, Y = Cl, Br, or I) are reported. The three totally symmetric fundamental vibrations of these complexes are identified. The extensive mixing of the symmetry coordinates that compose the symmetric normal modes expected in these systems is not observed. Instead the "group-frequency" approximation is valid. Furthermore, the force constants of both the apical and face-bridging metal-halide bonds are insensitive to the identity of either the metal or the halide. Raman spectra of related complexes with methoxy and benzenethiol groups as ligands are reported along with the structural data for [Mo(6)Cl(8)(SPh)(6)][NBu(4)](2). Crystal data for [Mo(6)Cl(8)(SPh)(6)][NBu(4)](2) at -156 degrees C: monoclinic space group P2(1)/c; a = 12.588(3), b = 17.471(5), c = 20.646(2) Å; beta = 118.53(1) degrees, V = 3223.4 Å(3); d(calcd) = 1.664 g cm(-)(3); Z = 2.