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PubMed2001

Enamel lead biomarker for prenatal exposure assessment.

The development of the enamel biomarker for heavy metal exposure assessment is designed to improve studies of dose-effect relationships to embryonic anomalies, particularly neurotoxic dysfunction. This report documents initial demonstrations of ambient lead (Pb) relative to calcium (Ca) in histological cross sections of deciduous tooth enamel of three human subjects, by use of ion mass spectrometry. The goal of this research was to measure Pb and Ca in tooth enamel for use as a temporal biomarker in assessing prenatal and postnatal exposure. This involves measurement of these heavy metals in enamel at high spatial resolution along histological transects following the temporal pattern of enamel growth. The technique may be applied when completely developed to cross-sectional and longitudinal research.

Biomarkers↗
PubMed1993

13C alpha-NMR assignments of melittin in methanol and chemical shift correlations with secondary structure.

Melittin is a naturally occurring hexacosa peptide which forms an amphiphilic helix in methanol, a random coil in water, and a tetramer of helices at basic pH or in the presence of a high salt concentration. The monomeric structure in methanol has been well characterized by proton NMR (Pastore et al. (1989) Eur. Biophys. J., 16, 363-367). In the present paper, chemical shifts of the backbone alpha-carbons of melittin in methanol were determined by mapping previously published alpha-proton shifts (Bazzo et al. (1988) Eur. J. Biochem., 173, 139-146), to natural abundance (1H)13C cross peaks appearing in the 2D heteronuclear multiple-quantum NMR spectrum. Changes in chemical shifts consequent to stepwise increases in the percentage of water in a mixed methanol/water solvent system were observed in similar spectra. The alpha-carbon shifts varied more smoothly than the corresponding alpha-proton shifts and were found to correlate with the transition from the helix to the random coil conformer in parallel with changes in the circular dichroism spectrum. Chemical shifts of this peptide are interpreted with regard to the current database of assignments in proteins of known 3D structure (Wishart et al. (1991) J. Mol. Biol., 222, 311-333). The N-terminal region of the peptide shows increased flexibility at lower methanol concentrations, as evidenced by the merger of the alpha-proton resonances of G1 (at 40% and 15% methanol) and G3 (at 15% methanol). Conformational exchange rates for G1 and G3 were estimated by comparison of the experimental spectra with simulated spectra and found to be as large as 4000 s-1 for G1 in 40% and 15% methanol and 600 s-1 for G3 in 15% methanol. Overall, these 1H and 13C chemical shift data support the description of monomeric melittin in methanol currently evolving in the literature and suggest a structure composed of a linked pair of helices with different structural stabilities, each of which experiences dynamical fraying at its free terminus.

Calcium Isotopes↗