Heavy Labeling of Recombinant Proteins
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Because of the cost of isotopic chemicals and heterologous proteins to produce, an economical 15 N/13 C isotopic labeling method is critically needed. Four protocols have been tested for the expression of Ovine interferon-τ in Pichia pastoris . 13 C-glucose in place of 13 C-glycerol as well as the need for 15 N/13 C-sources were evaluated during the growth phase. Sequential addition of 15 NH4 Cl and 13 C-methanol were also evaluated at different ratio. Our results demonstrate that 15 N/13 C isotopes are not required throughout the initial growth period but are necessary at low concentration a few hours prior to the methanol induction period. We have evaluated the cost of the use of isotopes 15 NH4 Cl, 13 C-glucose and 13 C-methanol in our optimised P4 protocol conditions. The cost was one-third that of the standard method using 15 NH4 Cl and 13 C-glucose throughout the entire growth period and was even lower using 13 C-glycerol.