Preparation of Thyroglobulin

Abstract

The method for preparing thyroglobulin has not been modified since Oswald described the procedure in 1899. He made saline extracts of fresh thyroid glands and precipitated the protein with an equal volume of ammonium sulfate. The process was time consuming since the precipitate had to be washed many times. Any other globulins present were also carried down and contaminated the final product. In attempting to prepare hog thyroglobulin, I found that the final preparation was frequently insoluble in saline or even dilute alkali. It was desirable to develop a more rapid method which would give a product suitable for intravenous injection. This has been accomplished by precipitating the thyroglobulin at the isoelectric point.

The fresh glands may be extracted with 0.1 M sodium acetate and the protein precipitated with dilute acetic acid. It has been found that sodium acetate will remove just as much of the iodine from fresh glands as sodium chloride. The optimum mixture for precipitation can be determined by setting up the following series of tubes:

To each tube is added 1 cc. of the sodium-acetate extract. In a few minutes the optimum precipitate can be observed. It has been found that the maximum quantity of iodine is precipitated in the tube giving the greatest quantity of precipitate. For hog thyroglobulin, tube No. 3 gives the best results. Using these proportions, a considerable quantity of extract can be precipitated at one time.

If a soluble preparation is desired, it is necessary to remove the precipitate and redissolve it in a short time. If it is allowed to stand for 24 hours, the protein is denatured and cannot be redissolved. However, after one or 2 hours, considerable precipitate has settled out.