β‐Agarases I and II from <i>Pseudomonas atlantica</i>

<jats:p>β‐Agarase I and II were characterised by their action on agar‐type polysaccharides and oligosaccharides.</jats:p><jats:p>β‐Agarase I, an endo‐enzyme, was specific for regions containing a minimum of one unsubstituted neoagarobiose unit [3,6‐anhydro‐α‐<jats:sc>l</jats:sc>‐galactopyranosyl‐(1 → 3)‐<jats:sc>d</jats:sc>‐galactose], hydrolysing at the reducing side of this moiety. Yaphe demonstrated that agar was degraded by this enzyme to neoagaro‐oligosaccharides limited by the disaccharide but with a predominance of the tetramer [Yaphe, W. (1957) <jats:italic>Can. J. Microbiol. 3</jats:italic>, 987–993]. β‐Agarase I slowly degraded neoagarohexaose but not the homologous tetrasaccharide. [1‐<jats:sup>3</jats:sup>H] Neoagarohexaitol was cleaved to neoagarotetraose and [1‐<jats:sup>3</jats:sup>H]neoagarobiitol. The highly substituted agar, porphyran was degraded to methylated, sulphated and unsubstituted neoagaro‐oligosaccharides which were invariably terminated at the reducing end by unsubstituted neoagarobiose.</jats:p><jats:p>The novel enzyme, β‐agarase II, was shown to be an endo‐enzyme. Preliminary evidence indicated this enzyme was specific for sequences containing neoagarobiose and/or 6<jats:sup>1</jats:sup>‐<jats:italic>O</jats:italic>‐methyl‐neoagarobiose. It degraded agar to neoagaro‐oligosaccharides of which the disaccharide was limiting and predominant. β‐Agarase II rapidly degraded isolated neoagarotetraose and neoagarohexaose to the disaccharide. With [1‐<jats:sup>3</jats:sup>H]neoagarohexaitol, exo‐action was observed, the alditol being cleaved to neoagarobiose and [1‐<jats:sup>3</jats:sup>H]neoagarotetraitol. Neoagarotetraitol was hydrolysed at 4% of the rate observed for the hexaitol. Porphyran was degraded to oligosaccharides, the neutral fraction comprising 24% of the starting carbohydrate. This fraction was almost exclusively disaccharides (22.4%) containing neoagarobiose (7.4%) and 6<jats:sup>1</jats:sup>‐<jats:italic>O</jats:italic>‐methyl‐neoagarobiose (15%). β‐Agarase II is probably the ‘β‐neoagarotetraose hydrolase’ reported by Groleau and Yaphe as an exoenzyme against neoagaro‐oligosaccharides [Groleau, D. and Yaphe, W. (1977) <jats:italic>Can. J. Microbiol. 23</jats:italic>, 672–679].</jats:p>