Milk proteins have largely been considered as providing
essential amino acids, but
oligopeptides derived from milk proteins have been shown to possess biological
functions. In vitro, opioid activity was first reported
in bovine β-casein hydrolysate
by Brantl et al. (1979). Precursors of biologically active
peptides have been
demonstrated in vivo after digestion of milk (Scanff
et al. 1992). Peptides that inhibit
platelet aggregation (Fiat et al. 1989), stimulate the
immune system (Migliore-Samour
et al. 1989), inhibit angiotensin I converting enzyme (Maruyama
& Suzuki, 1982) and
are involved in intestinal Ca solubilization and absorption (Sato
et al. 1986) have also
been isolated from bovine casein hydrolysates.
Bioactive peptides from whey proteins and their physiological effects
have
received less attention than those from casein. Peptides with opiate-like
activity
include the lactorphins, residues 50–53 in bovine and human
α-lactalbumin and 102–105 in bovine β-lactoglobulin (β-lg)
(Chiba & Yoshikawa, 1986; Yoshikawa et al.
1986; Antila et al. 1991). Yamauchi (1992) has reported
that a peptide derived from
β-lg induced contraction of guinea pig ileum longitudinal muscle
in the absence of
electric stimulation and agonist. The fragment, containing residues
146–149 of β-lg
(His–Ile–Arg–Leu), was called β-lactotensin.
The purpose of this study was to determine whether β-lactotensin
was released
from bovine β-lg by in vitro proteolysis using
different proteolytic enzymes. The
pharmacological activity of this tetrapeptide was characterized in guinea
pig ileum
in vitro using a synthetic fragment.