From Big Medical Encyclopedia

THIAMINASE — the enzyme which is selectively destroying and inactivating thiamin (vitamin B 1 ). At the person at food the products containing highly active T., a hypovitaminosis of B1 can develop (see. Beriberi ). T. crude fish is rich. Pathogenic intestinal microflora of the person — Clostridium thiaminolyticus, you. thiaminolyticus, you. aneurinolyticus — is also T. Sposobnostyyu's source to synthesize the enzyme destroying thiamin (see), Staphylococcus aureus, Proteus vulgaris, Salmonella possess also E. coli. For the first time T. it was found in connection with development of symptoms of avitaminosis of B1 (so-called chastekovsky paralysis) in the polar foxes getting crude fish on fur farms.

Distinguish two types T.: thiaminase of I (thiamin pyridinylazu, thiamin: основание-2-метил-4-аминопиримидин-5-метенил-трансферазу, KF, the catalyzing replacement of a tiazolovy component in a molecule of thiamin on any nitrogen base (e.g., pyridine), and a thiaminase of II (a thiaminase, thiamin-hydrolase; KF, on pirimidinovy and tiazolovy speak rapidly the molecule of thiamin hydrolytic splitting.

The thiaminase of I is present at tissues of many fresh-water fishes (representatives this are especially rich with it. cyprinid), nek-ry sea fishes, and also mollusks, in particular fresh-water swan mussel. It is found in a number of plants (e.g., in ferns) and in separate species of microorganisms. The thiaminase I allocated in a crystal view from you. thiaminolyticus, has a pier. the weight (weight) apprx. 40000 also shows the maximum activity at pH 6,5.

The thiaminase of II is revealed only at microorganisms so far. The thiaminase of II allocated in a crystal view from you. aneurinoeyticus 7 has a pier. weight apprx. 100 000 also shows a maximum of activity at pH 8,5 — 8,6. Both enzymes contain several sulphhydryl groups (see), important for their catalytic activity.

Activity of T. determine by a decrease of thiamin, education new derivative a pirimidinovy part of a molecule of thiamin with any nitrogen base (during the definition of activity of a thiaminase of I) or by eliminating of radioactive thiazol during the use as substrate of thiamin, marked 35 S.

Bibliography: Kochetov of G. A. Tiaminovye enzymes, M., 1978, bibliogr.; Ostrovsky Yu. M. Antivitamins in experimental and medical practice, Minek, 1973; Pokrovsky! A. A. Metabolic aspects of pharmacology and toxicology of food, M., 1979.

V. B. Spirichev.