Influence of pH on the appearance of active peptides in the course of peptic hydrolysis of bovine haemoglobin.

Influence of pH on the appearance of active peptides in peptic hydrolysis of bovine haemoglobin was studied in a homogenous phase system. Six active peptides were studied: three hemorphins: LVVH-7 (beta 31-40), VVH-7 (beta 32-40), VVH-4 (beta 32-37), one bradykinin-potentiating peptide (alpha 110-125), one antibacterial peptide (alpha 1-23), and neokyotorphin (alpha 137-141). The influence of pH was investigated in the course of the hydrolysis of haemoglobin by pepsin at 23 degrees C in acetate buffer at pH 3.5, pH 4.5, and pH 5.5. The hydrolysis of haemoglobin was studied in the presence or absence of urea. The haemoglobin hydrolysis at pH 4.5 is taken as a reference. Two different mechanisms of hydrolysis were observed: "one by one" for native haemoglobin hydrolysis at pH 4.5 and 5.5, and "zipper" for denatured haemoglobin at pH 3.5, pH 4.5, and pH 5.5, and native haemoglobin at pH 3.5. Whatever the pH and medium, a selectivity change by the pepsin was noticed. In the presence of urea, there are two phenomena: some peptides are preferentially produced at pH 3.5 and other peptides at pH 5.5, which seems to favour one particular site of pepsin that is cut. In the absence of urea, these active peptides reached a higher concentration at pH 3.5. In order to prepare these six active peptides, it is suitable to hydrolyse haemoglobin in the absence of urea at pH 3.5 (this pH denatures haemoglobin) where a "zipper" mechanism is obtained, and the peptide quantity is more significant at pH 3.5 than at pH 4.5.