Molecular Weight of Human Pituitary Gonadotropins as Determined by Radiation Inactivation of Biological Activity

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Abstract
Purification is not required to determine the molecular weight of protein hormones by means of radiation inactivation. Acetone-dried human pituitary powder, a urinary preparation from human castrate males (NIH-HPG-UE), and a urinary preparation from postmenopausal human females (Pergonal) were radiated with 2.0 mev electrons at varying doses. Loss of biological activity was measured by means of prostate and testes weight in hypophysectomized rats. When the loss of biological activity was plotted against radiation dose, exponential curves were obtained. These plots were identical for all 3 gonadotropin preparations and for each of the bio-assays. Molecular weight estimates of the gonadotropins in all 3 preparations were similar and averaged 31.4 × 103 (range 30.0–34.0), irrespective of which bioassay was used. Using identical methods, previous studies on human chorionic onadotropin have also resulted in molecular weight estimates of 30.4 × 103. It is concluded that human FSH, LH and chorionic gonadotropin have similar molecular weights of approximately 30,000.