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PubMed1985

Dynamics of calcium metabolism in infancy and childhood. I. Methodology and quantification in the infant.

The dynamics of calcium metabolism in the human infant were determined using stable isotopes of calcium as tracers. Two isotopes, one given intravenously and the other orally were used. Tracer time-dependent dilutions were measured with high accuracy and precision using thermal ionization mass spectrometry. Similar studies were performed in infant rhesus monkeys using radio tracers. Analysis of the isotope dilutions using a compartmental model method showed quite similar results for the infants of both species. These similarities support the validity both of using stable isotopes in human studies, and the use of the rhesus monkey as a model for human calcium dynamics. It was found that the classical steady state compartmental model was inadequate for use in the rapidly growing infant, and the model was modified to account for the expansion of the body fluid calcium compartment during the time of the study. Comparison with adult human calcium metabolic parameters showed that urinary calcium flows are much higher in the adult than in the newborn, relative to other calcium metabolic parameters. Other parameters of infant calcium metabolism are all consistent with the growth and more rapid metabolism usually seen in the young.

Absorption↗
PubMed1992

Conformational changes in the metal-binding sites of cardiac troponin C induced by calcium binding.

Isotope labeling of recombinant normal cardiac troponin C (cTnC3) with 15N-enriched amino acids and multidimensional NMR were used to assign the downfield-shifted amide protons of Gly residues at position 6 in Ca(2+)-binding loops II, III, and IV, as well as tightly hydrogen-bonded amides within the short antiparallel beta-sheets between pairs of Ca(2+)-binding loops. The amide protons of Gly70, Gly110, and Gly146 were found to be shifted significantly downfield from the remaining amide proton resonances in Ca(2+)-saturated cTnC3. No downfield-shifted Gly resonance was observed from the naturally inactive site I. Comparison of downfield-shifted amide protons in the Ca(2+)-saturated forms of cTnC3 and CBM-IIA, a mutant having Asp65 replaced by Ala, demonstrated that Gly70 is hydrogen bonded to the carboxylate side chain of Asp65. Thus, the hydrogen bond between Gly and Asp in positions 6 and 1, respectively, of the Ca(2+)-binding loop appears crucial for maintaining the integrity of the helix-loop-helix Ca(2+)-binding sites. In the apo- form of cTnC3, only Gly70 was found to be shifted significantly downfield with respect to the remaining amide proton resonances. Thus, even in the absence of Ca2+ at binding site II, the amide proton of Gly70 is strongly hydrogen bonded to the side-chain carboxylate of Asp65. The amide protons of Ile112 and Ile148 in the C-terminal domain and Ile36 in the N-terminal domain data-sheets exhibit chemical shifts consistent with hydrogen-bond formation between the pair of Ca(2+)-binding loops in each domain of Ca(2+)-saturated cTnC3.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗