Abstract
The importance of knowing the amino acid content of feed-stuffs has led the authors to apply Van Slyke's method 1 for the analysis of proteins direct, without previous isolation of the proteins themselves. The fine-ground and well-mixed material is weighed off in amount equivalent to 2-3 grams protein (estimated from the N-content) and completely hydrolyzed with 20 per cent. hydrochloric acid. Thereafter the method of Van Slyke is followed.
Analyses of corn, corn germ, cottonseed flour, kafir corn, tomato seed (pressed) and peat have been completed, results in duplicate agreeing well. The authors have had difficulty in accounting for the sulphur of the protein, the results for cystin being lower than was expected. This difficulty has been experienced by others and it is generally believed that if the cystin grouping be present, it is decomposed on hydrolysis and the sulphur changed to a form not precipitated by phosphotungstic acid with the cystin fraction. It is also conceded that sulphur exists in protein in other than the cystin grouping.
The results show Kafir corn and tomato seed meal to be lacking in histidin. Qualitative tests for tryptophan are positive for tomato seed, positive but slight for Kafir corn. Osborne and Clapp 2 found tryptophan and lysin, 2.93 per cent. in glutelin extracted from corn by weak alkali. The same investigators found neither lysin or tryptophan in zein of corn. Osbome's feeding experiments with cottonseed globulin show this protein to be satisfactory for maintenance and growth. Lysin and tryptophan are both present. Other experiments by Osborne and Mendel indicate that lysin and tryptophan in the diet are both necessary for growth. If lysin be present without tryptophan maintenance is secured, but not growth. The writers found lysin N in both corn and cotton seed.
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