The structure, role and representatives of phosphotransferases

Phosphotransferases, or kinases are one-component enzymes, but they have quaternary structure, i.e. consist of some subunits and therefore have got allosteric center. They catalyze phosphorylation. The source of phosphoric acid is ATP mainly. There are 2 types of phosphorylation – reversible and irreversible.

When the phosphoric acid joins with macroergic bond the phosphorylation is reversible.

Creatine+ATP↔creatinephosphate+ADP (enzyme is creatinekinase which is located mainly in skeletal muscles and heart). For example,

2ADP↔ATP+AMP (enzyme is adenilylkinase which is mostly located in skeletal muscles).

When the phosphoric acid joins without macroergic bond the phosphorylation is irreversible, e.g.:

Protein+ATPàphosphoprotein+ADP (enzyme is proteinkinase which is located in all tissues)

Glucose+ATPàglucose-6-phosphate+ADP

In some cases the source of phosphoric acid may be high energetic phosphorus containing substances. Such phosphorylation is named as substrate’s one:

Pyruvic acid+ATPàphosphoenolpyruvate+ADP (enzyme is phosphopyruvatekinase, or pyruvatekinase)

3-phosphoglyceric acid+ATP↔1,3-diphosphoglyceric acid+ADP (phosphoglyceratekinase)

The general characteristic of lyases

Lyases catalyze the reactions of cleavage of substrates without water or addition of some atoms on the position of double bonds. They are two-component enzymes and occur in cells. They’re divided into:

1) decarboxylases of ketoacids (apoenzyme + thyamin diphosphate)

2) decarboxylases of amino acids (apoenzyme + phosphopyridoxal)

3) carbonic anhydrase (apoenzyme + zinc)

The structure and catalytic role of decarboxylases of ketoacids

Decarboxylases of ketoacids consist of apoenzyme and coenzyme as thyamin diphosphate. Thyamin diphosphate is vitamin B1 + 2H3PO4

Decarboxylases of ketoacids enter the multi-enzymic complexes, e.g. pyruvate dehydrogenase’s complex which catalyzes the reaction of oxidative decarboxylation of pyruvic acid. The 3 main enzymes enter this complex: pyruvatedehydrogenase, pyruvatedecarboxylase (PDC) and acetyltransferase. First enzyme catalyzes the dehydrogenation (removal of hydrogen) of pyruvic acid; PDC catalyzes decarboxylation (removal of CO2); acetyltransferase enters the CoA in product of reaction. This reaction results in formation of acethylCoA (active acetic acid).

<== попередня сторінка	\|	наступна сторінка ==>
The general characteristic of transferases	\|	The structure and catalytic role of decarboxylases of amino acids

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