Study of the conversion of asparagine and glutamine of proteins into diaminopropionic and diaminobutyric acids using [bis(trifluoroacetoxy)iodo]benzene prior to amino acid determination

Abstract

The treatment of several proteins with [bis(trifluoroacetoxy)iodo]benzene (BTI) was examined as a possible way to determine separately their asparagine and glutamine content, through the quantification of their corresponding 2,3-diaminopropionic and 2,4-diaminobutyric acids. The diamino acid peaks were resolved between those of phenylalanine and lysine after a modification of the chromatographic conditions required for phenylthiocarbamylamino acid analysis. Rate studies performed on three proteins with BTI in the presence of dimethylformamide at 60 °C showed a maximum conversion of amides into diamino acids ranging from 50 to 83% after 4 h of contact, thereby making the direct quantification of amides in protein through the evaluation of diamino acids unsuitable; a fast (30 min) and virtually complete disappearance of glutamine; and a slower (2 h) and only partial (65 ± 6%) disappearance of asparagine.