The complete amino acid sequence of green turtle (Chelonia mydas) egg white ribonuclease

Egg white ribonuclease was first found in green turtle eggs. This enzyme has been purified by CM-toyopearl cation exchange. Two isoforms (GTRNase-1 and GTRNase-2) were further separated by RP-HPLC, with the same M.W. (13 kDa) and activity. These isoforms carried one amino acid exchange of Ser and Leu at the position 37. The N-terminal sequence, ETRYEKF, was determined for the transblotted protein. Internal sequences were analyzed by protein sequencer and ESI-Q-TOF mass spectrometry for tryptic peptides (Ts). The overlapping sequences were obtained from chymotryptic peptides, CNBr fragments and ISD-MS/MS analysis. The C-terminal Ile was identified by CPase-Y. The established sequence composed of 119 residues with the molecular mass of 12,942.1 Da for GTRNase-1 and 12,967.8 Da for GTRNase-2. The comparison of sequence with known pancreatic RNases, 27 positions including catalytic residues at the position 11 and 114 were conserved. Also basic residues contributed to phosphate binding residues were conserved with the exception of Lys 66. One insertion at the position 14, and 3 deletions at the position-1, between position 64-65, and 110 and 111 were found. Two Cys residues at position 65 and 72 that form a disulfide bond in mammalian RNase were deleted and exchanged. All these difference in the sequence were similar to reptile pancreatic RNase.