Some Analyses of Thyroglobulin

Abstract

In view of the physiological importance of thyroglobulin, it is somewhat surprising that little information has been made available concerning its amino acid composition. Until recently, the investigation of Eckstein 1 represented the only study, by more recent methods of protein analysis, of the distribution of the more important amino acids of thyroglobulin. The basic amino acids yielded on hydrolysis of this protein have been recently determined in this laboratory 2 by isolation procedures, and the results compared with those of Eckstein. Additional data have now been obtained regarding some of the other amino acids of thyroglobulin and are being presented inasmuch as further chemical investigation of this protein is not contemplated at the present time. A portion of these analyses supplement information already available in the literature; others represent the first determinations of certain of the amino acids of thyroglobulin.

The preparation used for this analytical work has been previously described. 2 Glutamic acid and aspartic acid were determined by the isolation procedure of Jones and Moeller. 3 The tyrosine and tryptophane determinations were conducted as described by Folin and Ciocalteau. 4 Proline was determined by utilizing the fractionation technique recently described by Jukes. 5 The percentage of proline is calculated from the weight of the analytically pure cadmium chloride salt, isolated as recommended by Kapfhammer and Eck. 6 Cystine analyses were conducted by 2 methods, the colorimetric procedure of Folin and Marenzi, 7 and the cysteine cuprous mercaptide method of Vickery and White. 8 Cystine values found by the 2 methods are in good agreement. The results of the various determinations, expressed as percentages of the ash- and moisture-free protein, are presented in Table I. Results already reported 2 are also included to provide the complete data which have been obtained for this protein in this laboratory.