Growth-active peptides are produced from α-lactalbumin and lysozyme

We determined the growth-active domains of milk-growth factor (MGF), human α-lactalbumin (HMLA) and human lysozyme (HMLZ), and their sequences. Fetal calf serum (FCS) showed inhibitors against proteases. The growth-stimulation of IMR90 cells in CG medium (free-serum) without FCS was induced in a dose-dependent manner up to 400 ng/ml of HMLA, HMLZ or chicken lysozyme (ChLZ), and also in a time-dependent manner until 48 h but was induced gradually until 1000 ng/ml of bovine α-lactalbumin (BVLA). The HMLAL6-peptide (HMLAL6), a cleaved product from HMLA by Endpeptidase Lys C, was growth-stimulative. The sequence of HMLAL6 was matched to 35 amino-acid residues (from No. 59 to No. 93 of HMLA), owing to the sequences of HMLAL6R3, HMLAL6R5 and HMLAL6R7 after the reduction of HMLAL6. The sequences of the reduced peptides from MGFL7-peptide (MGFL7: a cleaved product from MGF by Endpeptidase lysine C matched to those of the peptides from HMLAL6, and were similarly identified as the partial sequence of HMLA (59–93, H2N–L.W.C.?.K./S.S.Q.V.P.Q.S.R.N.I.?.D.I.S.?.D.K./F.L. D.D.D.I.T.D.D.I.M.?.A.–COOH). The sequence of HMLZ is similar to that of HMLA. HMLZT7-peptide (HMLZT7), a cleaved product of HMLZ by trypsin, was confirmed to have growth-stimulating activity and it's sequence was partially identified as Y. W.?.N.D.G.K.T.P.G.A.V.N.A.?.H.L. —, owing to the results of HMLZT7R1 (reduction of HMLZT7) and HMLZA7R2 (reduction of HMLZA7-peptide (HMLZA7) cleaved product of HMLZ by Endpeptidase Arg C) and is accordingly the sequence from No. 63 to No. 97 of HMLZ. Therefore, the peptides produced from LA and LZ by proteolysis may play a role of growth-stimulation.