13C Nuclear magnetic resonance chemical shifts, 1JC-C scalar coupling constants, spin-lattice relaxation times, and nuclear Overhauser effects were determined for taurine-[1, 2 13C] and a taurine-[1 13C] and taurine-[2 13C] mixture in the presence and absence of calcium. Ionization constants for taurine amino and sulfonic acid groups and chemical shifts of N-methylene and S-methylene carbons of the taurine cation, zwitterion, and anion were obtained from simultaneous least squares analysis of 13C titration curves of both taurine carbons. Comparison of taurine titration shifts to values for related compounds reveals some unusual electronic properties of the taurine molecule. Stability constants of 1:1 calcium complexes with taurine zwitterions and anions, as well as their 13C chemical shifts, were obtained by least squares analysis of titration curves measured in the presence of calcium. The stability constants of calcium-taurine complexes were significantly lower than previous values and led to estimates that only approximately one percent of intracellular calcium of mammalian myocardial cells would exist in a taurine complex. The implications of these results with respect to the effect of taurine on calcium ion flux are discussed.
Bibliographical noteFunding Information:
We would like to thank Professor Gerald E. Gauli for bringing to our attention some of the unsolved problems of the fin&on of t&e and for his constant encouragementd uring the course of this study_ This work was supported by the United States Department of Energy under contract No. W-31-IO9-ENG-38. 1*-T&e was made available from the Stable Isotope Resource, Los A&amos Scientific Laboratory through National Institutes of Health grant RR 00962.