CARBOHYDRATE ANALYSIS OF PORCINE THYROGLOBULIN ISOFORMS WITH DIFFERENT IODINE CONTENTS

To further validate the relationship between thyroid hormone formation and the carbohydrate structure of thyroglobulin (Tg), we reinvestigat ed the relationship between the iodine content and the asparagine-link ed oligosaccharide structures of porcine Tg. Purified porcine Tg was f urther separated into isoforms (Tg-F1, -F2 and -F3) with a DEAE-cellul ose ion-exchange chromatography column. The iodine residues, neutral s ugar and sialic acid were analyzed for the separated Tg isoforms and t heir asparagine-linked oligosaccharide structures were analyzed. The a sparagine-linked oligosaccharides' were released from Tg-F1, -F2 and - F3 by hydrazinolysis and each oligosaccharide was labeled with p-amino benzoic acid octyl ester (ABOE). The ABOE-labeled oligosaccharides fro m Tg-FI, -F2 and -F3 were analyzed for their relative content in oligo saccharides of each structure type by chemical methods and DEAE-and Co nA high-performance liquid chromatography (HPLC) columns. As a result, it was revealed that the Tg fraction eluted at higher-ionic strength from a DEAE-cellulose column is apt to contain more of each iodoamino acid, as well as total content of iodine, larger negative zeta-potenti al, conforming to sialic acid content in the Tg molecule and to a high er content of di-sialo-bi-antennary complex and to high mannose-type o ligosaccharides. These results support the conclusion that iodine orga nification of the Tg molecule is correlated with asparagine-linked oli gosaccharide completion. (C) 1997 Elsevier Science B.V.