Enzyme thiaminase – enzyme that cause thiamin deficiency

Thiamin is one of the water soluble B vitamins and is also known as vitamin B1. Thiamin requirement can be greatly increased with the consumption of anti-thiamin substances in foods. Substances with an anti-thiamin activity are fairly common in nature and include structurally similar antagonists as well as structure-altering antagonist and thiamin degrading enzymes (thiaminases).

Thiaminase can cleave the vitamin B1 (by cleaving the pyrimidine from the thiazole ring) and render it inactive. People have acquired vitamin B1 or thiamin deficiency by eating raw clams and raw fish as a major part of their diet. This antagonist is easily destroyed by cooking. Since thiaminase is heat-labile, the problem can be avoided by cooking the fish before adding the other diet ingredients.

There are two forms of this enzyme, thiaminase I sand thiaminase II. The presence of thiaminase was discovered in clams by Fujita and Matsukawa in 1942 and in fresh-water fish by Green (1941, 1942). The enzyme was name ‘thiaminase’ by Sealock and White in 1949.

The presence of thiaminase was recorded in many freshwater and saltwater fish. Among fresh-water fish, carp and crusian carp exceed other species in the potency of this particular enzyme, which is most abundant in kidneys, intestines and gills.

Heat processing destroys thiaminase, which destroys thiamin in fish, shellfish, brussels sprouts, and red cabbage. In countries where large amounts of fish are eaten raw, human thiamin deficiency may occur.
Enzyme thiaminase – enzyme that cause thiamin deficiency

Absorption and Transport of Thiamin

The bioavailability of thiamin occurring naturally in foods is believed to be high. Dietary sources of thiamine include: yeasts, pork, sunflower seeds, legumes, chicken, fish, beef, wheat germ, cereal products, lentils, potatoes, rice polishing and nuts.

Occasionally, however, anti-thiamin factor may be present in the diet. For example, thiaminases present in the raw fish catalyze the cleavage of thiamin, thereby destroying its activity.

These thiaminases are thermolabile, however and cooking of fish rendered the enzymes inactive. Other anti-thiamin factors that are thermostable may be found in tea and certain fruits and vegetables such as blueberries, black currents, Brussels sprouts and red cabbage.

Dietary thiamine is absorbed readily from jejunum and proximal ileum and is transported to tissues where it is converted to the active form, thiamine pyrophosphate (TPP).

Absorption of thiamin can be both active and passive, depending upon the amount of the vitamin presented for absorption.

At low physiologic concentrations, thiamin absorption is an active process. This Na+ dependent, carrier mediated absorption occurs primarily in the jejunum but can occur in other portions of the small intestine as well.

When intakes of thiamin are high, the absorption route is predominantly passive. The rate of thiamin absorption is always quite high except in the case of ethanol ingestion and/or folate deficiency.

Thiamine is carried by the portal blood to the liver. In normal adults, 20-30% of plasma thiamine is protein-bound all of which appears to be TPP. The transport of thiamine into erythrocytes seems to be facilitated diffusion process, whereas it enters other cells by an active process.

Thiamine uptake by active transport is highest in the jejunum and ileum, with both passive diffusion and active carrier-mediated transport.

Ethanol ingestion interferes with active transport of thiamin, and folate deficiency prevents the normal duplication of enterocytes, thereby decreasing absorption, both active and passive.

Conversion to the active coenzyme form requires adenosine triphosphate (ATP) and thiamin pyrophosphokinase, an enzyme found in the liver and brain (and perhaps in other tissue as well).

Another form of thiamin (thiamin triphosphate, or ATP) is synthesized in the brain by action of a thiamin diphosphate (ADP) – ATP phosphoryl-transferase.
Absorption and Transport of Thiamin

What is thiamin?

Thiamin (vitamin B1), consists of a pyrimidine ring and a thiazole moiety.  Thiamin also known as vitamin B1, and aneurin was the first B vitamin identified.

This vitamin is found widely distributed in foods, but the only foods considered good sources of thiamin are pork and whole grain or enriched grain products. The richest sources are yeasts, and liver, however, cereal grains comprise the most important dietary sources of the vitamin in most human diet.

Thiamin functions as coenzymes in the metabolism of carbohydrates and branched-chain amino acids.

Severe thiamin deficiency results in the nerve and heart disease beriberi; less severe deficiency results in nonspecific signs: malaise, loss of weight irritability and confusion.

Thiamin deficiency can arise in humans due to various reasons such as a genetic defect in the thiamin transporter, poor nutrition and diuretic treatment.

Alcoholism is often found correlated with thiamin deficiency. In addition, both alcoholism and thiamin deficiency are found associated with Wernicke-Korsakoff syndrome.
What is thiamin?

Vitamin B of Thiamin

The B vitamins are water soluble. Thiamin or vitamin B1, the structural formula consists of a pyrimidine ring and a thiazole moiety linked by a methylene (CH2) bridge.

Thiamin is essential for proper energy production in every cell of the body but especially in the heart and brain. This vitamin is involved in all bodily oxidations that lead to the formation of carbon dioxide. It is necessary for nerve function, appetite, and normal digestion. It is also required for growth, fertility, and lactation.

The need for thiamin was first realized in the late 1800s, by Dutchman, C. Eijkman, when it was discovered that fowl fed diet of cooked, polished rice developed neurologic problems.

The symptoms of vitamin deficiency are retardation of growth, palpitation and enlargement of the heart, and hypertension. Severe efficiency was discovered as the cause of a syndrome known as beri-beri.

Thiamin

The various effects of a disturbance of the nerve centers such as forgetfulness or difficulty in thinking are other manifestations of vitamin B1 deficiency.

The vitamin is often lacking in the diet because much of the naturally occurring amounts of it in food are destroyed during the processing of the food.

Thiamin is widely distributed in foods, including meat (especially pork), legumes and whole, fortified or enriched grain products, cereals and breads.

Yeasts, wheat germ and soy milk also contain significant amounts of the vitamin.

The RDA for adult men aged 19 years and older is 1.2 mgs; for adult women of the same age, the RDA is 1.1 mgs per day.

Thiamin intake recommendations are 1.4 mgs per day during pregnancy and 1.5 mgs per day during lactation.
Vitamin B of Thiamin