RADIOIODINATION OF TRANSFORMING GROWTH-FACTOR-BETA (TGF-BETA) IN A MODIFIED BOLTON-HUNTER REACTION SYSTEM

We have optimized the use of the Bolton-Hunter reagent to prepare I-12 5-labeled transforming growth factor-beta (TGF-beta). Conditions were developed to obtain monovalent modification of human-recombinant TGF-b eta2 (hrTGF-beta2) at a basic pH necessary for efficient protein acyla tion (greater-than-or-equal-to 26% of theoretical) while obviating the problems of TGF-beta aggregation/precipitation. The purified Bolton-H unter labeled hrTGF-beta2 had a specific activity of 1.8-2.1 muCi/pmol , and the I-125 label was fully acid-precipitable. [I-125]hrTGF-beta2 was electrophoretically indistinguishable from unlabeled starting mate rial and displayed full immunoreactivity with polyclonal anti-TGF-beta 2 antibody. Both hrTGF-beta2 and Bolton-Hunter-labeled [I-125]hrTGF-be ta2 inhibited the growth of mink lung epithelial cells with equal effi cacy. These data validate a modified conjugation-iodination method for TGF-beta and invite general use of the Bolton-Hunter reagent for iodi nation of other TGF-beta isoforms and peptides similarly susceptible t o precipitation/aggregation under standard Bolton-Hunter incubation co nditions.