Abstract
Two water-soluble arabinogalactan proteins (A-I and A-II) were isolated from 13 different vegetables and their molecular weight distribution and chemical properties were comparatively investigated. The molecular weights of A-I and A-II were in the range of 20-60×104 and 9-13×104, respectively. The contents of carbohydrate and protein of A-I were in the range of 75-85% and 15-25%, respectively, and the carbohydrate contents of A-II were slightly higher than those of A-I. In both A-I and A-II, the galactose/arabinose ratio varied from 0.5 to 2.0 among the various vegetables tested. The amino acid compositions of A-I and A-II were characterized by appreciable amounts of hydroxyproline and serine, both peculiar to arabinogalactan proteins, and high proportions of glycine and alanine. However, their hydroxyproline contents differed widely among the tested vegetables. It was found that 13 vegetables examined could be classified into three types depending on the contents, ratios and molecular weight distributions of A-I and A-II: Type A (stalk, fruit and light-colored leafy vegetables, shells of beans, and root vegetables), Type B (seeds of beans and Japanese butterbur stalk), and Type C (green-colored leafy vegetables). Comparative examination of the three different types of vegetables suggested that the arabinogalactan protein profile was primarily determined by the degree of tissue hardening (fiberization) and greening, or by a combination of their effects.
