The conformation of oxytocin in dimethylsulfoxide as revealed by carbon-13 spin-lattice relaxation times |
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Authors: | R Walter I C Smith R Deslauriers |
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Institution: | 1. Department of Physiology, Mount Sinai School of Medicine, New York, New York 10029, U.S.A. |
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Abstract: | Information was obtained on rates of overall molecular reorientation and segmental motion of amino acid sidechains of oxytocin in dimethylsulfoxide by determination of spin-lattice relaxation times (T1) at 25 MHz for carbon-13 in natural abundance in the hormone. The T1 values of the α-carbons of amino acid residues located in the 20-membered ring of oxytocin are all about 50 msec. The overall correlation time for the hormone backbone was estimated to be 8.8 × 10?10 sec. The sidechains of Tyr, Ile and Gln undergo segmental motion with respect to the backbone of the ring. The T1 value of the α-carbon of the Leu residue is greater than for any α-carbon in the ring, indicating an increased mobility of the backbone of the C-terminal acyclic peptide as compared to the ring. The β- and γ-carbons of the Pro residue undergo an exo-endo interconversion with regard to the plane formed by α-carbon, δ-carbon and N atom of the Pro pyrollidine ring. These data are discussed in light of results from other experimental and theoretical studies, including carbon-13 spin-lattice relaxation times for oxytocin in aqueous solution. |
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