A naturally occurring αs1‐casein‐derived peptide in bovine milk inhibits apoptosis of granulosa cells induced by serum‐free conditions

Several naturally occurring peptides in bovine milk were characterized by tandem mass spectrometry and Edman degradation. Chromatograms of peptide fractions (passed through an ultra‐filtration membrane, nominal molecular weight limit 3000) prepared from colostrum (collected immediately after parturition) and transitional milk (collected 5 days postpartum) showed that they were almost identical. In total, six peptides, α_s1‐CN (f16‐23) (RPKHPIKH), α_s1‐CN (f16‐24) (RPKHPIKHQ), α_s1‐CN (f17‐25) (PKHPIKHQG), α_s1‐CN (f46‐52) (VFGKEKV), α_s1‐CN (f94‐105) (HIQKEDVPSER), and β‐CN (f121‐128) (HKEMPFPK), were identified. One of the major peptides, the N‐terminal fragment of α_s1‐casein, varied structurally during early lactation: α_s1‐CN (f17‐25) (PKHPIKHQG) and α_s1‐CN (f16‐23) (RPKHPIKH)/α_s1‐CN (f16‐24) (RPKHPIKHQ) were found in colostrum and transitional milk, respectively. A chemically synthesized peptide, α_s1‐CN (f16‐23) (RPKHPIKH), inhibited apoptosis of bovine granulosa cells induced by serum‐free conditions in a dose‐dependent manner, in consequence of caspase‐3 and caspase‐9 suppressions. The physiological function of the peptide remains unclear, but it may have potential use as pharmaceutical agent and as an anti‐apoptotic agent in cell culture medium. Copyright © 2014 European Peptide Society and John Wiley & Sons, Ltd.