Isolation and characterization of hagfish thyroid iodoprotein by its non-thyroglobulin nature, very high iodine and carbohydrate contents and low hormone/iodine ratio.
We have characterized the thyroid iodoprotein of a hagfish, Eptatretus burgeri, one of the lowest marine vertebrates. The iodoprotein was not very homogeneous in its apparent molecular mass which decreased with the increase in hormone/iodotyrosine ratio. Four subfractions with an apparent molecular mass of about 400 kDa were purified from one major fraction by size-exclusion and Mono Q ion-exchange HPLC. The subfractions appeared to have the same peptide backbone, since they showed a single band with the same mobility as a 160-kDa protein in SDS/PAGE and the same amino acid composition. However they differed from each other in having increasing iodine contents (1.9% to 5.9% by mass of total amino acids) associated with the increase in hormonal iodine proportion (8.4% to 16.7% of total iodine) and carbohydrate content (35.6% to 53.5% by mass). These values are strikingly different from those of thyroglobulin with an iodine content of less than 1%, hormonal iodine of 20-40% and carbohydrate content of less than 10%. The amino acid composition of the hagfish iodoprotein, especially the cysteine content of less than 1%, was also entirely different from that of thyroglobulin. These results suggest that most, if not all, tyrosine residues of the hagfish thyroid glycoprotein with a less rigid structure are susceptible to an iodinating system, but hormone residues are formed by a much less efficient mechanism than those in thyroglobulin, when poorly iodinated.
Ohmiya
Y
Y
Department of Physical Biochemistry, Gunma University, Japan.
Suzuki
S
S
Kondo
Y
Y
D000596:Amino Acids / Q000032:analysis; D000818:Animals; D002241:Carbohydrates / Q000032:analysis*; D002850:Chromatography, Gel; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D002852:Chromatography, Ion Exchange; D004586:Electrophoresis / Q000379:methods; D006196:Hagfishes; D007455:Iodine / Q000032:analysis*; D007467:Iodoproteins / Q000302:isolation & purification*; D011506:Proteins / Q000032:analysis; D013961:Thyroid Gland / Q000032:analysis*; D013963:Thyroid Hormones / Q000032:analysis*; D014020:Tissue Extracts / Q000032:analysis
D000596:Amino Acids; D002241:Carbohydrates; D007467:Iodoproteins; D011506:Proteins; D013963:Thyroid Hormones; D014020:Tissue Extracts; D007455:Iodine