INTRODUCTORY. OUR knowledge of the enzymes which bring about the hydrolysis of the mannans is far less extensive than of-those by which other polysaccharides are hydrolysed. There is no doubt, however, that they play an important role in the metabolism of certain plants, more especially during the germination process. Moreover since mannans are readily digested in the animal organism, it is more than likely that such digestion is the result of enzyme action. It would seem therefore that enzymes capable of hydrolysing mannans
The space group of pinnoite has been determined unambiguously as P42 but the reflexions for 1 = O, h+k odd, are either absent or extremely weak showing that pseudo-symmetry is present, the space group conforming closely to P42/n. The structure, obtained by making use of this pseudosymmetry and employing Patterson sections and projections, has been refined by successive twodimensional syntheses and it is found that the B atoms are tetrahedrally surrounded by O atoms and that the Mg atom is at the centre of an octahedron of O atoms. This arrangement suggests that the chemical formula should no longer be written as MgO.B~O3.3 H20 but as MgB~O(OH)6. A surprising and noteworthy feature of the structure is the presence of long tubular voids running parallel to the c axis, an arrangement not normally found in borate compounds.
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