The work carried out this year represents a continuation and extension of earlier studies on the role of protein-bound carbohydrates in biological systems. Three separate areas have been examined. (a) Current concepts of the mechanism of tritiated borohydride reduction of carbohydrates have been challenged and found wanting. Reduction under controlled conditions revealed the specific radioactivity of the individual sugars to vary widely and to be a function of the spatial environment of the carbonyl group being reduced. (b) Further understanding of the mechanism relating congenital goiter with hyposialylated thyroglobulin (described in an earlier report) has been attained by the demonstration in a rat thyroid cell line that TSH down-regulates mRNA for the enzyme, alpha2,6 sialyltransferase. The latter is responsible for the major portion of thyroglobulin sialyl residues which in turn affects iodination and hormone production. (c) An examination of the putative presence and potential role of carbohydrate-bound nuclear proteins has been initiated. Attention has been centered on those proteins which are tightly bound to DNA and which can be recovered from hydroxylapatite-bound chromatin. Preliminary findings point to the presence of small amounts of galactose and galactosamine.
