Phosphorylation of proteins by dry-heating in the presence of pyrophosphate and some characteristics of introduced phosphate groups

Various proteins and dextrin were phosphorylated by dry-heating in the presence of pyrophosphate, and phosphate bonds characterised. The basic proteins were more highly phosphorylated than acidic proteins by dry-heating in the presence of pyrophosphate. The phosphorylated poly-l-lysine hydrobromide (PP-PLy) and lysozyme (PP-Lz) were more highly dephosphorylated than phosphorylated dextrin and ovalbumin (PP-OVA) by phosphatases, and the dephosphorylation of PP-PLy was much higher than that of PP-Lz. The phosphate bonds in all phosphorylated samples were stable during heating at 120 °C. The 31P NMR spectral data suggested that different types of phosphate bonds were introduced, and the N–P bond was suggested in PP-PLy. Some phosphorylated tryptic peptides from PP-Lz and PP-OVA were detected by mass spectrometry analysis. Furthermore, the introduced phosphate linkages in peptides from PP-Lz and PP-OVA were identified.