Transfer of I-131 and fluoresceinyl sialic acid derivatives into the oligosaccharide chains of IgG: A new method for site-specific labeling of antibodies

Biochemical modifications of IgG can help to avoid damages caused by oxidat ion or reduction. Terminal groups of the saccharide structures, located in the Fc-portion of IgG molecules, were modified by enzymatic reactions. IgG was pretreated with sialidase, to cleave bound sialic acid, and with galact osyltransferase, to increase the number of acceptor sites for transfer reac tions. Afterward, modified sialic acid derivatives were transferred enzymat ically into the oligosaccharide chains of IgG. Labeling was possible with s ialic acids modified in either position 5 or position 9. The usefulness of this method was demonstrated for radioactive and fluoresceinylated reagents , with yields up to 90% in 1 h. Immunological investigations have shown no influence on the immunoreactivity by the described modification of sacchari de structures. NUCL MED BIOL 26;4:383-388, 1999. (C) 1999 Elsevier Science Inc. All rights reserved.