A Neglected Constituent of Proteins, α-Amino-n-butyric Acid

Abstract

ALTHOUGH its presence in proteins has been reported several times^1-6, α-amino-n-butyric acid has not been generally accepted as a naturally occurring amino-acid, probably because no readily reproducible method for its isolation has yet been described. However, the isolation of its hydroxy homologue threonine⁷ suggests that α-amino-n-butyric acid may occur widely, since whenever a known hydroxy amino-acid occurs in any given protein, the corresponding simple amino-acid is usually present in even larger amounts. Accordingly, it seems probable that an appropriate fractionation of the alanine and valine fractions of a protein rich in threonine would yield appreciable amounts of α-amino-n-butyric acid. Hydrolysis should preferably be enzymatic, since prolonged heating with mineral acids has been found to liberate some nitrogen from the synthetic dl-α-amino-n-butyric acid⁸, while l-glutamic acid heated with alkalis decomposes to acrylic acid and α-amino-n-butyric acid⁹, so that misleading results would be obtained by alkaline hydrolysis of proteins. Preliminary work along these lines has been interrupted by the War.