Bracken fern, thiaminase

In people whose thiamin intake is marginal, colonization of the gastrointestinal tract with thiaminolytic microorganisms may be a factor in the development of beriberi. The thiaminases present in raw fish can result in so-called Chastek paralysis of foxes and mink, as a result of destruction of thiamin, and may be important in parts of the world where much of the apparent thiamin intake is from fish that is eaten raw or fermented. The polyphenols and thiami-nase in bracken fern can cause thiamin deficiency (blind staggers) in horses, and tannic acid in tea and betel nut have been associated with human thiamin deficiency. 

The thiamin deficiency that occurs with chronic consumption of raw fish results from the activity of thiaminase. Thiarriinase catalyzes the cleavage and thus destruction of the vitamin. The thiaminase content of various types of raw seafood has been measured (Hilker and Peters, 1966). Unfortunately, a reliable study of thiaminase in raw seafood is not yet available. Bracken ferns also contain thiaminase. Grazing animals such as sheep consume these ferns and develop thiamin deficiency. The deficiency results in brain lesiorrs in the animal and in the bending backward of the neck. Australians call this phenomenon "stargazing," The animal falls to the ground and pedals its feet in the air. 

Enzymes destroying thiamine have been encountered in some species in a number of fresh-water fish, in very few salt-water fish, in some shellfish and Crustacea, in bracken ferns and in three species of intestinal bacteria. They have all received the name of "thiaminase , but it is very probable that we have to do with several, different, enzymes >23 They all bring about a fission of the thiamine molecule, liberating the thiazole part, but only in one case, that of thiaminase of Bacillus aneurinolyticus Kimura el Aoyana, reasonable proof has been obtained of a hydrolytic fission, yielding both moieties of the vitamin molecule z-methyl-q-amino-S-hydroxymethylpyr-imidine and 4-methyl-5(/ -hydroxy)-ethylthiazole. 

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See also in sourсe #XX -- [ ]

See also in sourсe #XX -- [ ]

See also in sourсe #XX -- [ ]

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