3 ペプチド性植物細胞増殖因子phytosulfokine-αの単離と構造決定(口頭発表の部)

抄録

Proliferation of dispersed plant cells in culture is strictly dependent on cell density, and cells in a low density culture can only grow in the presence of conditioned medium (CM). No known plant hormones have been able to substitute for CM so far. In order to quantify mitogenic activity of CM. we examined conditions for the assay system using mechanically dispersed mesophyll cells of Asparagus officinalis L., and established a highly sensitive bioassay method. By use of this system, the mitogenic activity of CM prepared from asparagus cells was characterized: it was heat stable, susceptible to pronase digestion, and resistant against glycosidase treatment. On the basis of these results, the mitogenic activity in CM was purified 10^7-fold by column chromatography, and two factors named phytosulfokine-α and β(PSK-α and PSK-β)were obtained. By amino acid sequence analysis and mass spectrometry, structures of these two factors were determined to be sulfated pentapeptide (H-Tyr(SO_3H)-Ile-Tyr(SO_3H)-Thr-Gln-OH) and sulfated tetrapeptide (H-Tyr(SO_3H)-Ile-Tyr(SO_3H)-Thr-OH). PSK-α and PSK-β were prepared by chemical synthesis and enzymatic sulfation. The synthetic peptides exhibited the same activity as the natural factors confirming the structure for PSK-α and PSK-β mentioned above. This is the first study to demonstrate the actual structure of peptidal growth factors in the plant kingdom.