Iodinated FSH: Components and Their Properties

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Abstract
The composition of 125I-FSH has been examined by gel nitration of iodinated FSH, immediately after iodination, on a 90 × 2.5 cm G-100 Sephadex column. We present data on four FSH iodinations, with specific activities of approximately 1,6,12 and 36 μCi/μg FSH. Three peaks of radioactivity appeared after gel nitration. We suggest that Peak 1 consists of aggregates of FSH, Peak 2 consists of single molecules of FSH and Peak 3 consists of FSH subunits. In the iodination with the lowest specific activity (1 μCi/μg) only Peak 2 appeared. Peak 3 became increasingly more definite as the degree of iodination increased. Both the immunoreactivity and the testicular binding activity of the various fractions of 125I-FSH after gel filtration, were examined. The highest immunoreactivity and receptor binding activity were found in the Peak 1 region. There was a negligible amount of immunoreactivity and receptor binding activity in the Peak 3 region and an intermediate amount in the Peak 2 region. Possible explanations are given for the finding of greater immunoreactivity and receptor binding activity in the aggregates of FSH than in single molecules of iodinated FSH. Although in all four iodinations examined the degree of iodination was relatively low, there was an inverse correlation between the degree of iodination and the receptor binding activity found in Peaks 1 and 2 indicating that the receptor binding activity of FSH is very sensitive to damage during the iodination reaction. (Endocrinology94: 952, 1974)
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