The precursor cleavage of the antimicrobial peptide α107-136 into the bradykinin-potentiating peptide α110-125 during peptic hydrolysis of bovine haemoglobin was investigated by reverse phase high-performance liquid chromatography coupled with tandem mass spectrometry. The optimal conditions for the preparation of α107-136 and α110-125 were found to be low and high degrees of hydrolysis respectively. A total of six peptides were identified as being involved in the cleavage process. Moreover, the reaction network of these peptides was developed according to the sequence alignment and their release kinetics. The affinity of pepsin towards different peptide bonds of bovine haemoglobin was also compared based on data from the release kinetics of peptides. In addition, some potentially bioactive peptides were predicted by means of sequence analysis and secondary structure calculations.