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Rhamnogalacturonan (alpha)-L-Rhamnopyranohydrolase (A Novel Enzyme Specific for the Terminal Nonreducing Rhamnosyl Unit in Rhamnogalacturonan Regions of Pectin)

Two (alpha)-L-rhamnohydrolases with different substrate specificities were isolated from a commercial preparation produced by Aspergillus aculeatus. The first rhamnohydrolase was active toward p-nitrophenyl-(alpha)-L-rhamnopyranoside, naringin, and hesperidin and was termed p-nitrophenyl-(alpha)-L-rhamnopyranohydrolase (pnp-rhamnohydrolase). From the data collected, the enzyme seemed specific for the (alpha)-1,2- or (alpha)-1,6-linkage to (beta)-D-glucose. The pnp-rhamnohydrolase had a molecular mass of 87 kD (sodium dodecyl sulfate-polyacrylamide gel electrophoresis), a pH optimum of 5.5 to 6, a temperature optimum of 60(deg)C, and a specific activity toward pnp-(alpha)-L-rhamnopyranoside (pnp-Rha) of 13 units mg-1 protein. The second rhamnohydrolase, on the contrary, was active toward rhamnogalacturonan (RG) fragments, releasing Rha, and was therefore termed RG-rhamnohydrolase. The RG-rhamnohydrolase had a molecular mass of 84 kD, a pH optimum of 4, a temperature optimum of 60(deg)C, and a specific activity toward RG oligomers of 60 units mg-1 protein. The RG-rhamnohydrolase liberated Rha from the nonreducing end of the RG chain and appeared specific for the (alpha)-1,4-linkage to (alpha)-D-galacturonic acid. The enzyme was hindered when this terminal Rha residue was substituted at the 4-position by a (beta)-D-galactose. The results so far obtained did not indicate particular preference of the enzyme for low or high molecular mass RG fragments. From the results it can be concluded that a new enzyme, an RG (beta)-L-rhamnopyranohydrolase, has been isolated with high specificity toward RG regions of pectin. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Plant Physiology American Society of Plant Biologist
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