Characterization of recombinant human epidermal growth factor produced in yeast

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Abstract
Four different forms of human epidermal growth factor (h-EGF) are found in the cutlure medium of a recombinant strain of Saccharomyces cerevisiae. These forms were characterized after purification using a reverse-phase high-performance liquid chromatography. The most abundant form of secreted recombinant h-EGF has leucine at the carboxyl terminus and is identical with .gamma.-urogastrone. A second species is identical with the most abundant form except that it lacks the carboxy-terminal leucine. This form appears to be the product of a carboxypeptidase found in the growth medium. The other two forms of recombinant h-EGF are the respective oxidation products of the above where the single methionine residue has been converted to methionine sulfoxide. These four forms of recombinant h-EGF are fully active; they bind to the EGF receptor of A431 cells as well as stimulate mitotic activity of human foreskin fibroblasts with equal specific activity. The location of the disulfide bonds in the predominant form of recombinant h-EGF swas determined following digestion with thermolysin. The amino acid compositions of the resulting peptides showed that the placement of disulfide bonds in recombinant h-EGF is identical with that in murine EGF.