Relative quantitation analysis of the substrate specificity of glutamyl endopeptidase with bovine α-caseins

A bovine α-caseins' preparation digested with glutamyl endopeptidase (GE) at 37 and 50°C was quantitatively analysed with the isobaric tag for relative and absolute quantification (iTRAQ) technique using nano-LC-ESI-QTOF-MS/MS. Incubation temperature was shown to affect protein digestion. MS analysis of the digestion products indicated that phosphorylated peptides were less sensitive than non-phosphorylated peptides according to the MS intensities. GE hydrolysed Glu(51)-Tyr(52) and Glu(50)-Glu(51) in Glu(49)-Glu(50)-Glu(51)-Tyr(52) of bovine αs1-casein. The results herein helped to confirm the precise process of α-caseins' hydrolysis with GE, which is significant for quantifying the release of bio- and techno-functional peptides.