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 degrees 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 degrees 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 alpha-L-rhamnopyranohydrolase, has been isolated with high specificity toward RG regions of pectin.
Mutter
M
M
Wageningen Agricultural University, Department of Food Chemistry, The Netherlands.
Beldman
G
G
Schols
H A
HA
Voragen
A G
AG
D001230:Aspergillus / Q000201:enzymology; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D002241:Carbohydrates / Q000032:analysis; D006026:Glycoside Hydrolases / Q000302:isolation & purification / Q000378:metabolism*; D008969:Molecular Sequence Data; D010368:Pectins / Q000737:chemistry / Q000378:metabolism*; D012210:Rhamnose / Q000378:metabolism; D013379:Substrate Specificity
D002241:Carbohydrates; D010368:Pectins; D006026:Glycoside Hydrolases; C090357:p-nitrophenyl-alpha-L-rhamnopyranohydrolase; C090358:rhamnogalacturonan rhamnohydrolase; C022525:alpha-L-rhamnosidase; D012210:Rhamnose