Fred C. Koch 105 



Phosphotungstic acid precipitate. Another 40 grams of thyreoglobulin 

 were boiled with 25 per cent phosphoric acid for ninety-three hours. The 

 filtrate from the melanoidin precipitate and metaprotein, after removal of 

 the phosphoric acid by Ba(OH) 2 and the excess of barium by sulphuric acid, 

 was concentrated under diminished pressure to about 250 cc. This was 

 then freed from proteose and peptone by the Kutscher tannin method. 16 

 The filtrate finally obtained here after removal of the excess of lead was 

 boiled with BaCO 3 to remove the ammonia. The dissolved barium was 

 again removed by sulphuric acid. The filtrate after acidifying with H 2 SO 4 

 to 5 per cent strength was precipitated with phosphotungstic acid in the 

 usual way. The precipitate after thorough washing with 2.5 per cent phos- 

 photungstic acid solution was freed from phosphotungstic acid, barium and 

 sulphate in the usual way. Duplicate determinations on the dry amino- 

 acid mixture gave 0.0107 per cent and 0.0093 per cent iodine. 



Another phosphotungstic acid precipitate from a hydrolysis by H 2 SO 4 

 was worked up in the same way. This dry residue contained 0.0068 per cent 

 iodine. The two samples were mixed and designated as P.T.A. Ppt. 1. 

 This mixture contained 0.0073 per cent iodine. 



Phosphotungstic acid filtrate (1). This was freed from phosphotungstic 

 acid in the usual way. The amino-acid solution was evaporated to dryness. 

 Duplicate determinations on the dry amino-acid mixture gave 0.0024 per 

 cent iodine. 



Phosphotungstic acid precipitate (2) . This was obtained in the same way 

 as the above from the partial hydrolysis by 10 per cent sulphuric acid of 

 141. 6 grams of thyreoglobulin containing 0.511 per cent iodine. The puri- 

 fied dry residue by analysis contained 0.0043 per cent iodine. 



Phosphotungstic acid filtrate (2}. The filtrate from the above was treated 

 in the usual way. The dry purified amino-acid mixture left gave in dupli- 

 cate determinations 0.0045 and 0.0043 per cent iodine. 



Tetra-iodohistidine anhydride. Histidine was prepared from ox erythro- 

 cytes by the method of Frankel. 17 Various methods were employed in 

 trying to iodize the dichloride or the base itself but in no case were there 

 indications of true absorption of iodine, but rather decomposition of the 

 histidine. While this work was under way Pauly 18 published his obser- 

 vations with the same conclusions as to the difficulty or inability to iodize 

 histidine directly. At the same time, as stated above, he published his 

 observations on tetra-iodohistidine anhydride. Following the methods 

 given by Pauly 19 the preparation of the methyl ester of histidine dichloride 

 was carried out and from this the histidine anhydride by the Pauly 

 modification 20 of the Fischer and Zuzuki method. The histidine anhydride 

 was recrystallized from hot water a number of times to obtain the more 



"Zentralbl. f. PhysioL, xix, p. 504, 1905. 



17 Monatsh.f. Chem., xxiv, p. 230, 1903. 



18 Ber. d. deutsch. chem. Gesellsch., xliii, p. 2243, 1910. 



19 Zeitschr. f. physiol. Chem., Ixiv, p. 75, 1910. 



20 Loc. cit. 



