PEPTIDE DEGRADATION - EFFECT OF SUBSTRATE PHOSPHORYLATION ON AMINOPEPTIDASIC HYDROLYSIS

The effect of substrate phosphorylation on the susceptibility to exope ptidasic attack by leucyl aminopeptidase of swine kidney, alanyl amino peptidase from human Liver and aminopeptidase N of Escherichia coli wa s investigated using a synthetic heptapeptide (L-R-R-A-S-L-G) and its phosphorylated derivative. The enzyme-catalyzed products were analyzed by thin layer chromatography and electrophoresis. The sensitivities o f peptide and phosphopeptide to leucyl aminopeptidase digestion were t hen compared. Data obtained indicated that when phosphopeptide was use d as substrate one main product accumulated, which corresponded to the fragment A-S(P)-L-G, while unphosphorylated peptide was completely de graded to its constituent amino acids. Identical results were obtained using aminopeptidase N of E. coli. Using alanyl aminopeptidase as enz yme, the results obtained were essentially similar, since the exopepti dasic activity on the phosphorylated peptide was strongly hampered in the vicinity of phosphoseryl residue leading to accumulation of the sa me phosphorylated product, although this enzyme could not completely d egrade the unphosphorylated peptide. It was concluded that phosphoryla tion of substrates does effect enzymic degradation of proteins. Copyri ght (C) 1996 Elsevier Science Ltd.