Critique of the Foreman method for the estimation of the dicarboxylic acids in protein hydrolysates

Abstract

The lime-ethanol method of Foreman [1914a] for the estimation of aspartic and glutamic acids in the products of protein hydrolysis has found wide application, and in the hands 6f later workers has undergone various modifications in detail. Foreman recited the conditions that he considered necessary for the quantitative precipitation ofthe dicarboxylic acids as their Ca salts from the amino-acid mixture obtained by hydrolysing the protein with HCR. He * In a private communication to one of us (A. C. C.) Mr Foreman stated that in 1914 he was aware of the superior selectivity of the Ca salts and that his choice was deliberate. The contrary opinion of Town [1941] was based on experiments with gliadin, which contains very little basic-N.

The estimation of threonine and serine in proteins

“…This latter problem has been simplified by the development of the new procedure described later for the quantitative estimation of hydroxylysine, so that due allowance for the formaldehyde given by this base can be made. The data given later in Table 2, showing good equivalence between the NH3 and the total volatile aldehyde obtained on periodate oxidation of various protein hydrolysates, serve to reinforce the conclusion to be drawn from the researches of earlier workers (Dakin, 1941;Nicolet & Shinn, 1942;Bailey, Chibnall, Rees & Williams, 1943) that ,B-hydroxyglutamic acid, which would give ammonia but no volatile aldehyde, is not a constituent of the proteins concerned.…”

The Chemistry of the Proteins and Amino Acids

“…The resulting succinic acid is determined in the Warburg apparatus with the aid of succinic dehydrogenase. The values obtained for the aspartic acid content of casein compare fairly well with those from Chibnall's laboratory (31) and from microbiological assay (32). The method gives too high values in the presence of asparagine, since variable fr actions of this are converted to fumaric acid on methylation..…”

Quelques Techniques Nouvelles Pour L'Etude De La Structure Des Proteines

“…L'acide 8-hydroxyglutamique de Dakin se trouvait Bgalement sur la liste car on pensait A 1'6poque en avoir is016 des quantites substantielles A partir de la casBine (49,183)' de la lactalbumine (115)' de la gliadine (116) et de la zBine (50). Or, toute une sBrie de travaux plus recents nous ont appris que la substance decrite par Dakin n'est certainement pas de l'acide 0-hydroxyglutamique (51,166)' mais un melange fort complexe contenant certains produits de dismutation de l'acide aspartique et de la cystine (9). L'existence de la norleucine (1) est Bgalement devenue fort douteuse.…”