Arabinogalactan Protein from a Crude Cell Organelle Fraction of Phaseolus vulgaris L.

Sonication of a crude cell organelle fraction from hypocotyl tissue of dark-grown bean seedlings, and from suspension-cultured cells released a hydroxyproline-containing protein. The purification of this protein is described. It was found to be an arabinogalactan protein composed of 90% carbohydrate and 10% protein. The major sugars are galactose, arabinose, and uronic acids, and the major amino acids are hydroxyproline, serine, and alanine. Its molecular weight was estimated at 1.4 x 10(5) daltons and the isoelectric point at pH 2.3. The molecule is soluble in 5% trichloroacetic acid and can be precipitated with beta-galactosyl Yariv antigen. Pulse-chase experiments indicated that it was a secretory protein. The biosynthesis of arabinogalactan proteins is discussed.