Structure of plant cell walls. Purification and characterization of a beta-1,4-galactanase which degrades a structural component of the primary cell walls of dicots.

Wild type Bacillus subtilis, when grown on a soybean arabinan-galactan, secretes a beta-1,4-galactanase which has been purified more than 200-fold from the culture fluid. Affinity chromatography was the most effective step in a purification procedure which resulted in a preparation that contained only a single 40,000 molecular weight protein band upon sodium dodecyl sulfate-disc gel electrophoresis. The purified galactanase digests a beta-1,4-galactan purified from citrus pectin and digests partially the isolated cell walls of suspension-cultured sycamore cells. The predominant product of the enzymic degradation of the substrates tested is a 4-linked tetragalactose. Evidence is presented to support the hypothesis that the galactanase attacks its substrates in both an exo- and endo-manner. The products obtained upon galactanase digestion of the soybean arabianin-galactan demonstrate that the earlier proposal concerning the structure of this polysaccharide must be incorrect.