β‐Agarases I and II from Pseudomonas atlantica

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Abstract
β‐Agarase I and II were characterised by their action on agar‐type polysaccharides and oligosaccharides.β‐Agarase I, an endo‐enzyme, was specific for regions containing a minimum of one unsubstituted neoagarobiose unit [3,6‐anhydro‐α‐l‐galactopyranosyl‐(1 → 3)‐d‐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) Can. J. Microbiol. 3, 987–993]. β‐Agarase I slowly degraded neoagarohexaose but not the homologous tetrasaccharide. [1‐3H] Neoagarohexaitol was cleaved to neoagarotetraose and [1‐3H]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.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 61‐O‐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 [1‐3H]neoagarohexaitol, exo‐action was observed, the alditol being cleaved to neoagarobiose and [1‐3H]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 61‐O‐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) Can. J. Microbiol. 23, 672–679].