Natural abundance carbon 13 nuclear magnetic resonance spectroscopy of antifreeze glycoproteins.

Natural abundance 13C NMR spectroscopy (at 67.9 MHz) is used to study an aqueous solution of the antifreeze glycoproteins 3 to 6 from the Antarctic cod. Assignments of resonances to specific carbons of the known Ala-Ala-[beta Gal-(1 leads to 3)-alpha-N-acetylgalactosamine]Thr repeating unit are presented. Some of the carbons of the proline residues of glycoprotein 6 are also identified. Spin-lattice relaxation times (at 30 degrees C), linewidths (at 35 degrees C), nuclear Overhauser enhancements (at 35 degrees C), and the temperature dependence of chemical shifts (from 0 degrees to 75 degrees C) all strongly suggest that these antifreeze glycoproteins are predominantly or entirely flexible random coil polymers.