DETERMINATION OF TRYPTOPHAN IN PURE PROTEINS AND PLANT-MATERIAL BY 3 METHODS

The tryptophan content of three pure proteins and eight samples of plant material was determined by three different methods (1-3). Protein hydrolysis was performed in the presence of Ba(OH)2(1), NaOH(2) or pronase (3). The tryptophan released was isolated by gel filtration (1) or ion-exchange chromatography (2) or neither (3) and was assayed by colorimetry with ninhydrin (1, 2) or p-dimethylaminocinnamaldehyde (3). The tryptophan recovered from pure proteins averaged 99.0 (1), 94.3 (2) and 98.1% (3). Method 1 was found to yield the highest and least dispersed values for the tryptophan content of samples of plant material.