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Compound specific nitrogen isotope analysis of amino acids (AA CSIA) has been used to study the trophic ecology of many marine organisms because of its ability to characterize the [delta].sup.15N value at the base of a food web while simultaneously providing trophic position information from a single tissue sample of a consumer. Although application of this method is becoming more widely used in trophic studies, critical assumptions such as amino acid designation and trophic discrimination factors remain unresolved for many taxa and tissue types. In this study, we used captive green turtles (Chelonia mydas) in a controlled feeding study to determine and evaluate individual amino acid isotope fractionation patterns and trophic discrimination factors (TDFs) for skin and plasma. Our data build on findings from previous studies that show that the traditional paradigm of using glutamic acid and phenylalanine as trophic and source amino acids, respectively, for trophic position estimation is consistent for green turtles; we also provide evidence to support the potential utility of other combinations of amino acids for trophic position calculations. Green turtle TDFs for glutamic acid and phenylalanine were 4.0 ± 0.5 â° and 6.6 ± 0.7 â° for skin and plasma, respectively. We found serine to have the largest [DELTA][delta].sup.15N (turtle-diet discrimination) value of all amino acids in both skin and plasma, while lysine [DELTA][delta].sup.15N values were consistent for use as a source amino acid in skin and plasma tissue. We evaluated our TDFs by estimating trophic position of four sea turtle species using previously published amino acid isotope data. These results indicate that for green turtles, the traditional use of glutamic acid and phenylalanine along with a combination of trophic amino acids paired with lysine can provide robust trophic position estimates. Moreover, we highlight the taxa and tissue-specific nature of amino acid nitrogen isotope fractionation patterns in green turtle tissues and underscore that well-approximated TDFs can refine trophic position estimates for sea turtles., Author(s): Garrett E. Lemons [sup.1] [sup.2], Rebecca L. Lewison [sup.1], Jeffrey A. Seminoff [sup.2], Christina M. Coppenrath [sup.3], Brian N. Popp [sup.4] Author Affiliations: (1) grid.263081.e, 0000 0001 0790 1491, [...]

Purpose This study was performed to determine if there is an age-related specificity in the response of muscle protein metabolism to severe burn injury during acute hospitalization. This is a retrospective analysis of previously published data. Methods Nineteen adult and 58 pediatric burn-injured patients (age 43.3 ± 14.3 vs. 7.2 ± 5.3 years, adult vs. children) participated in stable isotope [ring-.sup.2H.sub.5]phenylalanine (Phe) infusion studies. Femoral arterial and venous blood samples and muscle biopsy samples were collected throughout the study. Data are presented as means ± standard deviation (SD). A p value less than 0.05 was considered statistically significant. Results Muscle net protein balance (NB) was higher in children (adult vs. children, -43 ± 61 vs. 8 ± 68 nmol Phe/min/100 ml leg volume, p < 0.05). Muscle protein fractional synthesis rate (FSR) was higher in children (adult vs. children, 0.11 ± 0.05 vs. 0.16 ± 0.10 %/h, p < 0.05). Leg muscle protein breakdown was not different between the groups (adult vs. children, 179 ± 115 vs. 184 ± 124 nmol Phe/min/100 ml leg volume, p > 0.05); synthesis rate was 134 ± 96 and 192 ± 128 nmol Phe/min/100 ml leg volume in adults and children, respectively (p = 0.07). Age significantly correlated with muscle protein NB (p = 0.01) and FSR (p = 0.02); but not with breakdown (p = 0.67) and synthesis (p = 0.07) rates measured by using a three-pool model. Conclusion In burn injury, the muscle protein breakdown may be affected to the same extent in adults and children, whereas synthesis may have age-related specificities, resulting in a better but still low NB in children., Author(s): Demidmaa Tuvdendorj [sup.1] [sup.3], David L. Chinkes [sup.1] [sup.3], Xiao-Jun Zhang [sup.1] [sup.3], Arny A. Ferrando [sup.4], Itoro E. Elijah [sup.1] [sup.3], Ronald P. Mlcak [sup.1] [sup.3], Celeste C. [...]

In a systematic study of molecular recognition of amino acid derivatives in solid-state [beta]-cyclodextrin ([beta]-CD) complexes, we have determined crystal structures for complexes of [beta]-cyclodextrin/N-acetyl-L-phenylalanine at 298 and 20 K and for N-acetyl-D-phenylalanine at 298 K. The crystal structures for the N-acetyl-L-phenylalanine complex present disordered inclusion complexes for which the distribution of guest molecules at room temperature is not resolvable; however, they can be located with considerable confidence at low temperature. In contrast, the complex with N-acetyl-D-phenylalanine is well ordered at room temperature. The latter complex presents an example of a complex in this series in which a water molecule is included deeply in the hydrophobic torus of the extended dimer host. In an effort to understand the mechanisms of molecular recognition giving rise to the dramatic differences in crystallographic order in these crystal structures, we have examined the intermolecular interactions in detail and have examined insertion of the enantiomer of the D-complex into the chiral [beta]-CD complex crystal lattice.

We present a rapid and selective method to increase the volatility of tyrosine and phenylalanine without adding derivative C for high-precision gas chromatography--continuous-flow isotope ratio mass spectrometry (GCC--IRMS) based on enzymatic decarboxylation to yield alkylamines and evaluated for [sup.15]N isotopic integrity. Purified tyrosine and phenylalanine were converted to tyramine and phenethylamine by tyrosine and phenylalanine decarboxylases, respectively. GC separation was achieved using a thick stationary phase (5-[micro]m) capillary column. Recoveries were 95 [+ or -] 2%. The reproducibility of [delta][sup.15]N of tyramine and phenethylamine measured by GCC--IRMS averaged SD([delta][sup.15]N) = 0.33 [per thousand]. The absolute differences between [delta][sup.15]N of amino acids measured by elemental analyzer-IRMS and the alkylamines measured by GCC--IRMS was not significant. Phenethylamine and tyramine prepared from a mixture of 18 amino acids were extracted by ethanol with 95% recovery, and analysis yielded clean chromatograms and equivalent precision. These data indicate that enzymatic decarboxylation of phenylalanine and tyrosine is a convenient method to increase their volatility for continuous-flow isotopic analysis without introducing extraneous C or significant isotopic fractionation.

Isothermal titration calorimetry and site-directed mutagenesis were used to investigate the interaction of phenylalanine with the Escherichia coli P-protein catalyst. Findings furnished evidence for an independent regulatory domain in the P-protein that is spatially and functionally distinct from the catalytic domains. Certain P-protein mutants suggest that the process of phenylalanine-induced feedback inhibition involves distinct structural elements within the R-domain that are coupled, perhaps by an obligatory phenylalanine-induced conformational change.

Few techniques are amenable to real-time analysis of enantiomers. In this paper, total complexation by [Alpha]-acid glycoprotein (AGP) is shown to discriminate between enantiomers of dansyl-D,L-phenylalanine (DPs) by changing the local environment of the D and L enantiomers (DDP and DLP, respectively) from hydrophilic to hydrophobic. DDP and DLP show the same native fluorescence at [[Lambda].sub.ex]/[[Lambda].sub.em]=200/544 nm in the absence of AGP, but show shifted emissions with a component at [[Lambda].sub.ex]/[[Lambda].sub.em] = 220/497 nm in the presence of AGP and in lipophilic solutions. The conditions for an analytical determination have been optimized, and the method has been used to measure the enantiomeric composition of DDP/DLP mixtures with concentration ratios varying over 2 orders of magnitude. The mechanism of chiral recognition for DDP and DLP by AGP is discussed and should be equally applicable to other dansyl-derivative amino acid enantiomers. The association constants for AGP with DDP and with DLP have been determined to be 1.33 x [10.sup.2] L [g.sup.-1] and 2.29 x [10.sup.2]L[g.sup.-1], respectively.

Circular dichroism spectroscopic monitoring of the secondary structure of antimicrobial peptides in diphosphocholine micelles was used to determine the influence of the size of the nonpolar domain and of phenylalaline substitution at positions a and d on the stability and aggregation state of the coiled-coil in solution. Results have shown that phenylalanine interplay stabilizes the self-aggregation of cationic peptides. The aromatic residues, however, may restrict the side-chain formation resulting to possible destabilization of the helix.

Thermodynamic studies of the conformational changes in the wild type and in F31YA and F31Y mutants have depicted the effect of phenylalanine 31 in maintaining the conformational stability of ribonuclease P2 from Sulfolobus solfataricus under extreme conditions of temperature and pressure. Results have shown that the function of the protein determines the structural integrity which protects it from denaturation secondary to extreme conditions of temperature and pressure.

The effects of mutation of tyrosine 34 on the active site pK of reduced iron-containing superoxide dismutase was determined through the utilization of NMR spectral studies of the oxidized state and of the paramagnetically shifted resonances of the reduced state. Results have shown that the tyrosine mutated at 34 was partially responsible for the pH dependence of Fe-SOD activity and determines pK of the active site of Fe2+-SOD.

A new procedure for the interpretation of NMR relaxation data in terms of intramolecular motion is presented. First, a long molecular dynamics simulation of the system is produced and examined with respect to nuclear spin relaxation-active motional modes. Second, an analytical model is constructed based on the computational results. Last, the model parameters are determined numerically by a least-squares fit to the experimental NMR data.