Isolation and characterization of pokeweed mitogen-like phytomitogens from Shoriku, Phytolacca esculenta

From saline extracts of Phytolacca esculenta (shoriku) roots, two phytomitogenes were isolated by salting out with (NH4),SO4 and chromatography on DEAE-cellulose and Sephadex G-100 columns. Both fractions were homogeneous on disc electrophoresis and on immunoelectrophoresis. One of these (Fraction E-2) was shown to be similar to pokeweed mitogen in respect to mol. wt (32,000) and amino acid composition. The other (Fraction E-3) was a protein of 18,000 mol. wt. Both fractions had similar biological activities to pokeweed mitogen in their ability to stimulate pig blood lymphocytes in vitro to incorporate tritiated thymidine, and to induce blastoid transformation. Both fractions contained an unusually large amount of cystine, i.e., 18 half-cystine residues % for Fraction E-2 and 22 residues % for Fraction E-3. Although these mitogens were resistant to deproteinizing procedures such as perchloric acid treatment and Sevag's procedure, the DNA synthesis-stimulating activity was inactivated by digestion with Pronase E and Nagarse, but resistant to trypsin, chymotrypsin, deoxyribonuclease, ribonuclease, lysozyme and neuraminidase. The activity was stable at acidic and neutral pH (4-7) but unstable at alkaline pH. The activity at pH 7.3 was stabilized by the addition of Ca2+ or Mg2+. On the addition of more than 2 mM of Ca2+, precipitation of mitogen occurred. From the above results the molecular basis of the mitogenic activity of shoriku mitogen is discussed.