It has been found that Ser His could cleave bovine serum albumin(BSA), with the most suitable pH around 6.0. The kinds of buffers have different influences on the cleavage activity. The phosphate buffer and BR buffer are the most effective. The hydroxyl group of the serine residue is the essential functional group for the cleavage, while the amide bond, imidazole, and carboxyl group of Ser His increase the cleavage activity.
In this work, the change of gas-phase proton affinity of alkyl-alanine through the phosphorylation reaction was studied by the electrospray ionization mass spectrometry with kinetic method. It was proved that the phosphorylation could increase the proton affinity of small peptide. A proposal that proton affinity increase might be responsible for the sensitivity improvement of small peptide in mass spectrometry has been provided.
