The general characteristic of transferases

Transferases catalyze the reactions of transfer of atoms groups from one substance to another. They’re mainly two-component enzymes, i.e. consist of apoenzyme and coenzyme. They’re contained in cells only.

On the depend on transported atoms groups they’re divided into:

1) aminotransferases (apoenzyme + phosphopyridoxal)

2) methyltransferases (apoenzyme + tetrahydrofolic acid)

3) acyltransferases (apoenzyme + HSCoA)

4) phosphotransferases, or kinases (no coenzyme)

Aminotransferases consist of apoenzyme and coenzyme (phosphopyridoxal). Phosphopyridoxal is vitamin B6 + H3PO4.

Aminotransferases catalyze the transamination:

alfa-ketoglutaric acid + alanine↔pyruvic acid + glutamic acid (enzyme – alaninetransferase. It is mostly located in liver, heart and skeletal muscles).

Another reaction of transamination is:

alfa-ketoglutaric acid + aspartic acid↔oxaloacetic acid + glutamic acid (enzyme – aspartateaminotransferase. It is mostly located in heart, liver and skeletal muscles).

The importance of transamination:

1) this is the pathway of formation of unessential amino acids

2) transamination associates protein metabolism with carbohydrate metabolism

3) this is initiate stage of amino acid catabolism

4) aminotransferases are specific enzymes which occur in some organs. Lesion of rgans results in exit of aminotransferases in blood. It is important for diagnostic aims.

The structure, role and representatives of methyltransferases

Methyltransferases consist of apoenzyme and coenzyme as tetrahydrofolic acid (THFA). THFA is reduced vitamin Bc which consists of paraaminobenzoic acid, glutamic acid and pteridine.

Methyltransferases catalyze the methylation. Vitamin B12 helps this reaction. The source of CH3-group is methionine:

Norepinephrine+ methionineàepinephrine+homocysteine

ethanolamine+3methionineàcholine+3 homocysteine

uracil+methionineàthymine+homocysteine

The structure, role and representatives of acyltransferases

Acyltransferases consist of apoenzyme and coenzyme (HSCoA):

HSCoA consists of pantothenic acid, adenosine-3phosphate, thioethylamine, phosphate

Acyltransferases catalyze the acylation (transfer of residues of carboxylic acids):

Free fatty acid+HSCoA+ATPàAMP+H4P2O7+acive fatty acid

<== попередня сторінка	\|	наступна сторінка ==>
Table 5. Glycosidases	\|	The structure, role and representatives of phosphotransferases

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