Comparison of three signals for secretory expression of recombinant human midkine in Pichia pastoris

The secretion signals of Saccharomyces cerevisiae alpha mating factor, huma n midkine itself, and Pichia pastoris acid phosphatase, were tried for the expression of human midkine under the control of the AOX1 gene promoter in A pastoris. Approximately 28 mg/l, 1.5 mg/l, and 0.2 mg/l of midkine were s ecreted by using the alpha mating factor pre-pro-sequence, the midkine sign al sequence, and the phosphatase signal sequence in flask cultures, respect ively.