Abstract
The convincing evidence offered by Womack and Rose 1 that phenylalanine is essential in nutrition makes it desirable to know the phenylalanine content of the common food proteins. Moreover, a knowledge of the amino acid composition of purified proteins (or even of one purified protein) would be of immense value in formulating an adequate theory of protein structure. The last reported analysis of egg albumin for phenylalanine that the present authors have found was that of Osborne, Jones, and Leavenworth. 2 These authors, using the Fischer esterification method, 3 obtained 5.07 g of phenylalanine from 100 g of egg albumin. Previous workers had reported 2.5% (Fischer 4 ), 4.4% (Abderhalden and Pregl 5 ), and 5.2% (Hongounenq and Morel 6 ).
Egg albumin was isolated by the method of Cole. 7 After 2 re-crystallizations it was dialyzed in the apparatus described elsewhere. 8 The protein was air-dried and kept in a desiccator over phosphorus pentoxide. Its nitrogen content was 15.13% (see Calvery 9 and Arnow 10 ); a solution of it in distilled water had a pH of 4.75; and 98% of it in solution could be coagulated by heat.
Phenylalanine was determined by a modification of the Kapeller-Adler 11 procedure. The results are summarized in Table I.
If egg albumin is assumed to have a molecular weight of 40,500 (Svedberg 12 ), the data obtained suggest that one molecule of egg albumin contains 13 phenylalanine residues. On the other hand, adoption of the theory of Bergmann 13 would make it appear probable that one molecule of protein contains 12 phenylalanine residues; and the calculated molecular weight of egg albumin would be 37,300.
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