Characterization of Recombinant Rhamnogalacturonan -l-Rhamnopyranosyl-(1,4)--d-Galactopyranosyluronide Lyase from Aspergillus aculeatus¹
An Enzyme That Fragments Rhamnogalacturonan I Regions of Pectin

Margien Mutter, Ian J. Colquhoun, Gerrit Beldman, Henk A. Schols, Edwin J. Bakx, and Alphons G.J. Voragen^*

Wageningen Agricultural University, Department of Food Chemistry, Bomenweg 2, 6703 HD Wageningen, The Netherlands (M.M., G.B., H.A.S., E.J.B., A.G.J.V.); and Institute of Food Research, Norwich Laboratory, Norwich Research Park, Colney, Norwich NR4 7UA, United Kingdom (I.J.C.)

The four major oligomeric reaction products from saponified modified hairy regions (MHR-S) from apple, produced by recombinant rhamnogalacturonan (RG) -l-rhamnopyranosyl-(1,4)--d-galactopyranosyluronide lyase (rRG-lyase) from Aspergillus aculeatus, were isolated and characterized by ¹H-nuclear magnetic resonance spectroscopy. They contain an alternating RG backbone with a degree of polymerization of 4, 6, 8, and 10 and with an --(4,5)-unsaturated d-galactopyranosyluronic acid at the nonreducing end and an l-rhamnopyranose at the reducing end. l-Rhamnopyranose units are substituted at C-4 with -galactose. The maximum reaction rate of rRG-lyase toward MHR-S at pH 6.0 and 31°C was 28 units mg¹. rRG-lyase and RG-hydrolase cleave the same alternating RG I subunit in MHR. Both of these enzymes fragment MHR by a multiple attack mechanism. The catalytic efficiency of rRG-lyase for MHR increases with decreasing degree of acetylation. Removal of arabinose side chains improves the action of rRG-lyase toward MHR-S. In contrast, removal of galactose side chains decreased the catalytic efficiency of rRG-lyase. Native RG-lyase was purified from A. aculeatus, characterized, and found to be similar to the rRG-lyase expressed in Aspergillus oryzae.

Plant Physiol. (1998) 117: 141-152
Copyright Clearance Center:   0032-0889/98/117/0141/12
© 1998 American Society of Plant Physiologists

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