One or more serum factors promote peptide utilization in cultured animal cells

We have shown previously that MACT-T and C2C12 cells utilize methionine-containing di- to octapeptides as methionine sources for protein accretion and cell proliferation in the presence of 60 mL/L desalted fetal bovine serum. In this study, serum factors that may regulate the use of peptides as amino acid sources in C2C12 and MAC-T cells were examined. The basal media contained methionine-free Dulbecco's modified Eagle's medium supplemented with 4.0 mL/L bovine serum lipids, 10 mL/L chemically defined lipid concentrate, bovine insulin (1 mg/L), 30 mL/L low protein serum replacement (LPSR-1) or 60 mL/L desalted animal serum. Treatment media included basal media supplemented with no methionine, L-methionine, or one of the methionine-containing peptides. L-Methionine promoted protein and DNA accretion (P < 0.05) in the presence of desalted animal sera, insulin or LPSR-1. Methionine-containing peptides also promoted protein and DNA accretion (P < 0.05) in the presence of desalted animal sera or LPSR-1, but not with insulin, except methionylleucine. In a cell-free medium, fetal bovine serum hydrolyzed peptides to varying degrees. We conclude that animal sera contain one or more factors that regulate utilization of peptides as amino acid sources for C2C12 and MAC-T cells.