Chemical characterization of α hormones of Phytophthora parasitica

A method for the large scale hormone α1 and α2 extraction from agar cultures of A1 and A2 mating types of Phytophthora parasitica has been developed. Using a total of 240 L of organic solvents to extract 40 L of the agar medium, sufficient amounts of α hormones were obtained to permit characterization of their physical and chemical properties. Activities of both hormones were in the neutral fractions in acid-base partition. These hormones were not precipitated by cold acetone or digitonin, nor were their activities destroyed by saponification. Fractionation on an aminopropyl column showed that both hormones were neutral lipids with polarity similar to that of monoglycerides and that α2 had a polarity greater than that of α1. Both hormones were stable at 200°C under nitrogen, and α1 was more volatile than α2. After acetylation, the hormonal activity of α1 was retained, while that of α2 was greatly reduced. Base hydrolysis of the acetylated α2 led to the restoration of its hormonal activity. Using semi-preparative gas chromatography, α1 activity was eluted between 230 and 278°C while α2 could not be eluted under the same conditions. Results from this study suggest that α hormones are not phospholipids, glycolipids, glycerides, or steroids, but that they are probably neutral lipids with hydroxyl functional group(s). Structural elucidation of α1 and α2, however, would require an even greater scale of operation than that provided by the present experiment.