Thiaminase

There are two types of thiaminase ^[1] :

1. Thiaminase I ( eng. Thiamine pyridinylase ) - Code КФ 2.5.1.2 - the most common type. It acts by displacing nitrogenous pyrimidine methyl groups or an SH compound to break the thiazole ring.
Synonyms of Thiaminase I:
Proteins: pyrimidine transferase , thiamine hydronase
Alternative name: thiamine base 2-methyl-4-aminopyrimidine-5-methyltransferase ( eng. Thiamine: base 2-methyl-4-aminopyrimidine-5-methenyltransferase )

2. Thiaminase II ( Eng. Aminopyrimidine aminohydrolase ) - Code КФ 3.5.99.2 - this type acts through the hydrolytic cleavage of methylene-thiazole-H compounds with the formation of pyrimidine and thiamine fragments.
Synonyms of Thiaminase II:
Proteins: anevrinase (ust.), Anserinase (ust.), Thiamine hydronase
Alternative name: 4-amino-5-aminomethyl-2-methylpyrimidine hydrolase ( eng. 4-amino-5-aminomethyl-2-methylpyrimidine hydrolase )
Gene: tenA ( Locus : BSU11650)

When thiamine is cleaved, both types of thiaminase use cosubstrates (usually amine or sulfhydryl- containing compounds). For example, proline or cysteine .

A complete list of natural sources of thiaminase has not yet been determined. The enzyme is presented in several forms and is proven to be found in the tissues of many freshwater and marine fish. It is especially abundant in carp , Atlantic herring , and mollusks (Type I) ^[2] .
Thiaminase is found in the cells of animals and humans - normally it regulates the content of the corresponding coenzymes . It is produced by bacteria of the intestinal tract - Bacteria thiaminolytic and Bacteria anekrinolytieny (Type II) ^[3] . The source of thiaminase can be Staphylococcus aureus , Salmonella , Proteus, and some strains of E. coli . These thiamine-destroying bacteria are detected in the intestines of children suffering from eating disorders, as well as in adults with chronic gastrointestinal diseases.
The enzyme was found in African silkworm ( Anaphe venata) ^[4] and in a number of plants, for example, bracken fern, bog tail (Type I) ^{[5] [6]} .

The participation of thiaminase in the development of vitamin B ₁ deficiency was revealed in the study of a number of enzootic and endemic , arising without any epizootic and epidemiological connection between the previous diseases of people, animals and fish:

• Vitamin deficiency B ₁ was detected during a survey of Thai people who use raw fish in large quantities in their diet ^[7] ;
• The disease and death of fish (mainly from vitamin deficiency B ₁ ) was observed and experimentally confirmed under the influence of toxins of blue-green algae containing thiaminase. Eating sick fish is one of the versions of the manifestation of Haff disease ;
• Signs of diseases caused by a lack of thiamine were found in fur farms after raw carp were included in the diet of foxes ^[8] .

Thiaminase is destroyed by heating, but its types differ in heat resistance. Heat treatment of products containing thiaminase allows you to use them in food without fear of developing a thiamine deficiency. Australian aborigines soak marsilia rich in thiaminase for a long time before making soup or traditional “backgammon” cakes, since thermal treatment of fern thiaminase does not completely destroy them.
Animals suffering from thiamine deficiency due to eating thiaminase respond well to treatment in the early stages of the disease. Intramuscular injections of thiamine and removal of the source of thiaminase from the animal’s diet, as a rule, are sufficient for their full recovery ^[1] .

Thiaminase is relatively widespread in nature, which indicates the essential role of the enzyme in maintaining cellular metabolism , despite the negative effect of the enzyme. The enzyme breaks down vitamin B ₁ in the body, but does not break down thiol derivatives of thiamine. Since the thiol form under the action of acid forms thiamine again, when the thiaminase level is uncritically exceeded, this creates the possibility of maintaining the amount of thiamine necessary for the body. ^[9]