thumb|[[Thiamine]]

Thiaminase is an enzyme that metabolizes or breaks down thiamine into pyrimidine and thiazole. It is an antinutrient when consumed.

The old name was "aneurinase".

There are two types with different Enzyme Commission numbers:

  • Thiamine pyridinylase, Thiaminase I (, )
  • pyridine + thiamine <=> 5-(2-hydroxyethyl)-4-methylthiazole + heteropyrithiamine
  • Secreted by Paenibacillus thiaminolyticus, an anaerobic organism that occurs in the human small intestine
  • Aminopyrimidine aminohydrolase, Thinaminase II (, , )
  • 4-amino-5-aminomethyl-2-methylpyrimidine + H<sub>2</sub>O <=> 4-amino-5-hydroxymethyl-2-methylpyrimidine + NH<sub>2</sub><sup>+</sup> In bacteria, it stays inside their cells. These periplasmic binding proteins have two domains that each contain an α/β fold. These two domains come together to form a deep cleft that are connected by three crossover segments. Due to this structure scientists proposed that Thiaminase I could have evolved from prehistoric periplasmic binding protein that had been responsible for up taking thiamin.

Thiaminase II

Thiaminase II cleaves but does not add a base compound. Thiaminase II can only use water as the nucleophile.

Thiaminase II has been found to be TenA. In order to cleave the C-N bond between the thiazole and pyrimidine Thiaminase only uses water as its nucleophile. When viewing Thiaminase II it is found to have a crystal structure that has 11 helices surrounding a deep acidic pocket. The consumer eventually will fall ill, even die, from a thiamine deficiency. This has been seen in different lab studies. Through these studies the enzyme has been found in zebra fish as well as red cornet fish. nardoo,

  • Fish including zebra fish,
  • Bacteria such as Paenibacillus thiaminolyticus (formerly in Bacillus), Clostridium sporogenes,
  • An African silk worm, Anaphe venata; this enzyme is more heat-tolerant than other thiaminases and requires a longer cooking time

Sources of thiaminase II include:

  • Bacillus aneurinolyticus and Bacillus subtilis.

Effects

Function

It is still unclear what thiaminase does for fish, bacterial cell or insects that contain it. In ferns, thiaminase I is thought to offer protection from insects

Studies have shown that thiamine hydrolase (thiaminase II), which was originally thought to be involved solely in the degradation of thiamine, has actually been identified as having a role in thiamine degradation with the salvage of the pyrimidine moiety. Thiamin hydrolysis product N-formyl-4-amino-5-aminomethyl-2-methylpyrimidine is transported into the cell and deformylated by the amidohydrolase ylmB and hydrolyzed to 5-aminoimidazole ribotide.

When ingested

It was described in 1941 as the cause of highly mortal ataxic neuropathy in farmed foxes fed with raw carp.

It was once causing economical losses in raising fisheries, e.g. in yellowtail fed raw anchovy as a sole feed for a certain period, and also in sea bream and rainbow trout. The same problem is being studied in a natural food chain system.

The larvae of a wild silk worm Anaphe venata are being consumed in a rain forest district of Nigeria as a supplemental protein nutrition, and the heat-resistant thiaminase in it is causing an acute seasonal cerebellar ataxia named African seasonal ataxia or Nigerian seasonal ataxia.

In 1860–61, Burke and Wills were the first Europeans to cross Australia south to north; on their return they subsisted primarily on raw nardoo-fern. It is possible that this led to their death due to the extremely high levels of thiaminase contained in nardoo. The Aborigines prepared nardoo by soaking the sporocarps in water for at least a day to avoid the effects of thiamine deficiency that would result from ingesting the leaves raw. In the explorers' journals they noted many symptoms of thiamine deficiency, so it is thought that they did not soak the nardoo long enough. Eventually thiamine deficiency could have led to their demise.