Hydrolysis of oligopeptides by sera used in cell and tissue culture

Sera commonly used in cell and tissue culture as medium supplements possess high peptidase activity. Pligopeptides incubated with 1% serum are rapidly hydrolyzed to intermediate length peptides and the constituent amino acids. Hydrolysis of lysine peptides is difficult to verify by a quantitative ninhydrin procedure because of reaction of the lysine epsi-lon-amino group and serum components with ninhydrin. Attempts to evaluate oligopeptides as sole sources of indispensable amino acids for cultured mammalian cells are of doubtful value when serum is used as a medium supplement.