Mannitol Dehydrogenase from Agaricus Campestris.

Enzymes capable of catalyzing n-mannitol formation from n-fructose or n-fructose 6-phosphate have been identified in various microorganisms. Substrate and coenzyme specificity have been established in only a few instances, but there appear to be enzymes, dependent upon nicotinamide adenine dinucleotide and upon nicotinamide adenine dinucleotide phosphate, which reduce fructose directly to mannitol. An example of the former, a specific mannitol dehydrogenase from Lc~!~ba.cillus brewis, has been described recently by Martinez, Barker, and Horecker (1). Matitol formation in another group of microorganisms has been shown to be brought about indirectly by a phosphatase-catalyzed hydrolysis of mannitol-1-P formed from fructose-6-P by an NAD-dependent dehydrogenase (24). n-Mannitol, and other polyols as well, are widely distributed in plants, and it has generally been assumed that they originate from sugars by reduction. The simultaneous occurrence of n-mannitol and n-fructose in the brown algae, for example, has led to the suggestion that an enzyme catalyzing their interconversion may be present.’ Aside from the observation that extracts of So&us aucaparia berries possess NAD-linked dehydrogenase activity toward sorbitol and n-mannitol (6), no work has been reported on mannitol dehydrogenases in plants or higher fungi. This, together with the recent demonstration by Hughes, Lynch, and Somers (7) that n-mannitol is present to the extent of some 18% of dry weight in the cultivated mushroom, Agaricus campestris, led us to examine this system.2