Determination of tryptophan in pure proteins and plant material by three 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.