Characterization of α‐casozepine, a tryptic peptide from bovine α s1 ‐casein with benzodiazepine‐like activity

ABSTRACT Caseins are a known source of biologically active peptides. In this study, we have shown evidence of a novel anxiolytic activity in a tryptic hydrolysate of bovine α s1 ‐casein. Injection of 3 mg/kg of this hydrolysate significantly reduced the epileptic symptoms caused by pentylenetetrazole in rats. Anxiety reduction was also observed when the hydrolysate was tested in the elevated plus‐maze and in the conditioned defensive burying rat models. Peptides isolated from the hydrolysate were examined for their affinity for the γ‐amino‐butyric acid (GABA) type A receptor. Only one peptide, named α‐casozepine, corresponding to the 91–100 fragment from bovine α s1 ‐casein, expressed affinity for GABA A receptor. In vitro , the peptide had 10,000 less affinity for the benzodiazepine site of the GABA A than did diazepam. However, in the conditioned defensive burying paradigm it was 10‐fold more efficient than diazepam. The difference observed between the in vitro and in vivo activity of α‐casozepine could not been explained by an action via the peripheral‐type benzodiazepine receptor; α‐casozepine had no affinity for this receptor. The α‐casozepine amino acid sequence could be related to the carboxy‐terminal sequence of the polypeptide diazepam binding inhibitor, an endogenous ligand of the central GABAA and peripheral‐type benzodiazepine receptors.