Reaction: Hydrolysis of β-D-galactopyranose-(1→4)-α-L-galactopyranose-6-sulfate linkages in porphyran
Other name(s): porphyranase; PorA; PorB; endo-β-porphyranase
Systematic name: porphyran β-D-galactopyranose-(1→4)-α-L-galactopyranose-6-sulfate 4-glycanohydrolase
Comments: The backbone of porphyran consists largely (~70%) of (1→3)-linked β-D-galactopyranose followed by (1→4)-linked α-L-galactopyranose-6-sulfate [the other 30% are mostly agarobiose repeating units of (1→3)-linked β-D-galactopyranose followed by (1→4)-linked 3,6-anhydro-α-L-galactopyranose] . This enzyme cleaves the (1→4) linkages between β-D-galactopyranose and α-L-galactopyranose-6-sulfate, forming mostly the disaccharide α-L-galactopyranose-6-sulfate-(1→3)-β-D-galactose, although some longer oligosaccharides of even number of residues are also observed. Since the enzyme is inactive on the non-sulfated agarose portion of the porphyran backbone, some agarose fragments are also included in the products . Methylation of the D-galactose prevents its binding at position -1 .
Links to other databases: BRENDA, EXPASY, KEGG, Metacyc, CAS registry number:
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2. Correc, G., Hehemann, J.H., Czjzek, M. and Helbert, W. Structural analysis of the degradation products of porphyran digested by Zobellia galactanivorans β-porphyranase A. Carbohydrate Polymers 83 (2011) 277-283.