Hydrolysis of proteins using dipeptidyl aminopeptidases: analysis of the N-terminal portion of spinach plastocyanin

Abstract

The exopeptidases dipeptidyl aminopeptidases I and IV [DAP I and DAP IV] were used to hydrolyze the N-terminal portion of spinach plastocyanin to dipeptides. The enzymes were used individually as well as in a mixture and the dipeptides were analyzed by combined gas chromatography-mass spectrometry. Data are presented for native plastocyanin and the S-methylated protein. Of the 98 residues which make up this protein, the first 44 were released in the form of 22 dipeptides by the combined action of DAP I and DAP IV. These dipeptides were aligned by homology to other plastocyanins of known sequence. The results demonstrate the versatility of the 2 enzymes in hydrolyzing proteins to obtain information on their primary sequence.