Separation of a thyroid‐active fraction from unheated soya bean flour

An agent depressing thyroid function present in soya beans has been described. It is soluble at pH 4.2, in 2 vol. of acetone and 10% trichloroacetic acid and insoluble in 90% acetone, 90% ethanol and in ethyl ether. It is not precipitated by saturated ammonium sulphate and resists pancreatic digestion and boiling for 2 h, but is apparently destroyed by autoclaving. Evidence of its small molecular weight includes its dialysability and retardation on a Sephadex G25 column. It decreases iodine uptake by the thyroid gland and its incorporation into the diet increases the tri‐iodothyronine‐binding capacity of rat serum.