Fission of Peptide Bonds by Lithium Borohydride

Abstract

THE value of lithium aluminium hydride as a reagent for the characterization of the C-terminal residues of proteins has been investigated by several workers¹; but, except in the case of insulin², the potentialities of lithium borohydride have been less fully explored. Grassmann, Hörmann and Endres³ have described a method for the characterization of the C-terminal residues of small peptides which involved esterification followed by reduction with lithium borohydride hydrolysis and identification of the amino-alcohols produced. When a similar technique was applied to procollagen⁴, amino-alcohols were obtained even from the un-esterified protein and it was concluded that carboxylic ester groupings were present. Experiments carried out in this laboratory and described below show, however, that cleavage of peptide bonds can be brought about by lithium borohydride, those bonds involving the carboxyl group of glycine or of alanine being particularly susceptible. At present, therefore, little confidence can be placed in lithium borohydride as an end-group reagent for large peptides or proteins.