Enzymic synthesis of 3:6-anhydro-l-galactose within porphyran from l-galactose 6-sulphate units

Abstract

The liberation of sulphate from the ester linkages of porphyran, which is catalysed by an enzyme preparation from Porphyra extracts, is inseparable from the simultaneous synthesis of 3:6-anhydrogalactose units within the polysaccharide. The enzymic reaction is seen to be analogous to the well-known alkaline elimination of sulphate from hexose 6-sulphate derivatives. It is suggested that L-galactose 6-sulphate units in porphyran are converted, with fission of the C-0 bond of the sulphate ester, into 3:6-anhydro-L-galactose residues and that the enzyme is therefore not a true sulphatase. The biosynthesis and structure of porphyran are discussed in the light of the characterization of this enzyme. During the normal processes of collecting, drying and extracting the seaweed, the enzyme does not modify porphyran to any measurable extent. The enzyme shows diminished activity towards the products of partial acidic and enzymic hydrolysis of porphyran, and its action is not reversible.