Despite the importance of coastal ecosystems for the global carbon budgets, knowledge of their carbon storage capacity and the factors driving variability in storage capacity is still limited. Here we provide an estimate on the magnitude and variability of carbon stocks within a widely distributed marine foundation species throughout its distribution area in temperate Northern Hemisphere. We sampled 54 eelgrass (Zostera marina) meadows, spread across eight ocean margins and 36° of latitude, to determine abiotic and biotic factors influencing organic carbon (Corg) stocks in Zostera marina sediments. The Corg stocks (integrated over 25‐cm depth) showed a large variability and ranged from 318 to 26,523 g C/m2 with an average of 2,721 g C/m2. The projected Corg stocks obtained by extrapolating over the top 1 m of sediment ranged between 23.1 and 351.7 Mg C/ha, which is in line with estimates for other seagrasses and other blue carbon ecosystems. Most of the variation in Corg stocks was explained by five environmental variables (sediment mud content, dry density and degree of sorting, and salinity and water depth), while plant attributes such as biomass and shoot density were less important to Corg stocks. Carbon isotopic signatures indicated that at most sites <50% of the sediment carbon is derived from seagrass, which is lower than reported previously for seagrass meadows. The high spatial carbon storage variability urges caution in extrapolating carbon storage capacity between geographical areas as well as within and between seagrass species.

The goal of this study is to use the model system described earlier to make direct measurements of the enthalpy of helix formation at different temperatures. For this we studied model alanine peptides in which helix formation can be triggered by metal (La 3؉ ) binding. The heat of La 3؉ interaction with the peptides at different temperatures is measured by isothermal titration calorimetry. Circular dichroism spectroscopy is used to follow helix formation. Peptides of increasing length (12-, 16-, and 19-aa residues) that contain a La 3؉ -binding loop followed by helices of increasing length, are used to separate the heat of metal binding from the enthalpy of helix formation. We demonstrate that (i) the enthalpy of helix formation is ؊0.9 ؎ 0.1 kcal͞mol; (ii) the enthalpy of helix formation is independent of the peptide length; (iii) the enthalpy of helix formation does not depend significantly on temperature in the range from 5 to 45°C, suggesting that the heat capacity change on helix formation is very small. Thus, the use of metal binding to induce helix formation has an enormous potential for measuring various thermodynamic properties of ␣-helices. The year 2001 marked the 50th anniversary of the ␣-helix, the first proposed protein secondary structure (1). However, despite numerous efforts (see refs. 2-5 and references therein), the detailed thermodynamic basis for helix formation and for the helix propensities of the amino acids is not yet well understood. Accurate values for such basic thermodynamic parameters as the changes in enthalpy and heat capacity on helix formation are still under debate. Recently Bierzynski and coworkers (6, 7) developed a peptide system for inducing helix formation by adding a metal ion. They took a 12-residue sequence, analogous to a Ca 2ϩ -binding loop from calmodulin (peptide P1), which forms a short and very stable C-terminal helix, containing three to four residues, when the peptide binds La 3ϩ . The C-terminal segment of La 3ϩ -bound P1 provides a stable helical nucleus for helix propagation when additional residues are added at the C terminus. Bierzynski and coworkers also made a longer peptide (P2) with three additional alanine residues plus one C-terminal glutamine residue, and determined the NMR structure of the La 3ϩ -ligated form. Their model system should allow accurate determination of the enthalpy of helix formation by using ITC (isothermal titration calorimetry) to monitor stepwise, La 3ϩ -induced helix formation, and we exploit this potential here.Helix-coil transitions of short peptides in water cannot usually be described by a two-state model because the helix propagation constant is not large enough. For this reason, and also because the enthalpy change on helix formation is not large, temperatureinduced helix unfolding spans a very broad temperature range, which makes it difficult to determine the baseline. Analysis of thermal helix-coil transitions can be based on the Zimm-Bragg or Lifson-Roig theories (e.g., see ref.2), but the enthalpy values determined in t...

Very short alanine peptide helices can be studied in a fixed-nucleus, helix-forming system [Siedlicka, M., Goch, G., Ejchart, A., Sticht, H. & Bierzynski, A. (1999) Proc. Natl. Acad. Sci. USA 96, 903-908]. In a 12-residue sequence taken from an EF-hand protein, the four C-terminal peptide units become helical when the peptide binds La 3؉ , and somewhat longer helices may be made by adding alanine residues at the C terminus. The helices studied here contain 4, 8, or 11 peptide units. Surprisingly, these short fixed-nucleus helices remain almost fully helical from 4 to 65°C, according to circular dichroism results reported here, and in agreement with titration calorimetry results reported recently. These peptides are used here to define the circular dichroism properties of short helices, which are needed for accurate measurement of helix propensities. Two striking properties are: (i) the temperature coefficient of mean peptide ellipticity depends strongly on helix length; and (ii) the intensity of the signal decreases much less rapidly with helix length, for very short helices, than supposed in the past. The circular dichroism spectra of the short helices are compared with new theoretical calculations, based on the experimentally determined direction of the NV 1 transition moment.A long-standing goal in the study of peptide helices has been to relate the properties of helix formation in standard peptides (for example, in alanine-based peptides; refs. 1-3) to those observed when the helix is initiated by a helical template or an actual fixed helical nucleus (4-7). The first results obtained by using a synthetic template to initiate helix formation (4-6) showed little relation to the results found with standard peptides. In particular, alanine residues added to the synthetic template were reported (4-6) to have a lower helix propensity than in alanine-based peptides. The synthetic template used in these initial studies was acetyl-L-Pro-L-Pro, only one of whose three conformers is productive in initiating a helix (4-6). Bierzynski and coworkers (7) succeeded in nucleating short alanine-rich helices with a helical nucleus obtained by binding La 3ϩ to a 12-residue peptide (P1) modeled on an EF-hand protein. The four C-terminal peptide units become helical when P1 binds La 3ϩ , and longer helices can be made by adding residues at the C terminus of P1. The NMR structure (7) of a second peptide P2, with four additional residues (A 3 Q) added to, P1 defines the structure of the fixed helical nucleus, and agrees with earlier work (8) on the ligands that coordinate La 3ϩ . All but one of the participating ligands lie outside the helix in the N-terminal direction; the side-chain -COOH group of Glu 12, inside the helix, participates in binding La 3ϩ . Recently, Bierzynski and coworkers made an extensive study of helix propagation in this system (to be published), and they found a helix propensity for alanine in good agreement with results from standard alaninebased peptides (A. Bierzynski, personal communication).Circular dich...

Anhand sichtbarer und 1H‐NMR‐ spektroskopischer Untersuchungen wird die Bildung eines neuen Intermediärprodukts bei der Zugabe von Disauerstoff zu Toluollösungen von FeL bei ‐80°C nachgewiesen.

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Sir:Currently, ion-molecule reactions are the objects of intense investigations. Results from these studies have proven to be valuable in expanding the availability of gas-phase thermochemical values such as electron affinities and heats of formation. In particular, data from the study of ion-neutral association reactions provide a foundation for understanding subjects such as ion solvation, atmospheric ion chemistry, nucleation phenomena, and ion-molecule interactions.1.2Recently, Robbiani and Franklin3 have reported upper limits to the heats of formation of SO2CIand (SO2)2CI-based on observations of the ion-molecule reactions CI-+ s o 2 c 1 2 -SO2CI-+ c 1 2 (1) SO2CI-+ S02Cl2 -S204CI-+ Cl2 (2) From these reactions, they compute AHfo(S02CI-) I -136

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The refolding kinetics of the 140-residue, all ␤-sheet, human fibroblast growth factor (hFGF-1) is studied using a variety of biophysical techniques such as stoppedflow fluorescence, stopped-flow circular dichroism, and quenched-flow hydrogen exchange in conjunction with multidimensional NMR spectroscopy. Urea-induced unfolding of hFGF-1 under equilibrium conditions reveals that the protein folds via a two-state (native 7 unfolded) mechanism without the accumulation of stable intermediates. However, measurement of the unfolding and refolding rates in various concentrations of urea shows that the refolding of hFGF-1 proceeds through accumulation of kinetic intermediates. Results of the quenchedflow hydrogen exchange experiments reveal that the hydrogen bonds linking the N-and C-terminal ends are the first to form during the refolding of hFGF-1. The basic ␤-trefoil framework is provided by the simultaneous formation of ␤-strands I, IV, IX, and X. The other ␤-strands comprising the ␤-barrel structure of hFGF-1 are formed relatively slowly with time constants ranging from 4 to 13 s.