Absolute stereo chemical relative

Substrate specificityis named “absolute” were the enzymes acts on one substrate only, f.e. maltase acts on maltose, only.

Substrate specificity is named “relative” when the enzyme acts on the group of substrates, which have the same type of linkage, f.e α- amylase acts on starch and glycogen. These substrates have the same type of linkage.

Substrate specificity is named “stereo chemical” when the enzymes catalyzed the reaction with one from possible stero isomers of substrate f.e. enzyme fumarathydrotase catalyzed the hydration of fumarate and doesn’t act on maleniate. Fumarate and maleniate are stereoisomers of gulantadioic acid. Fumarate is trans –isomers, maleniate- is a cys- isomer.

The specificity of action of enzymes is an ability of enzymes to catalyzed specific reaction. The enzymes many possess the same substrates specificity, but each from them catalyzed only specific reaction with substrate, f.e. multienzymatic complex in which the enzymes act, but each of them catalyzed the specific reaction, f.e pyruvate dehydrogenase complex has got at least 3 enzymes:

-pyruvate dehydrogenase (PDH)

- pyruvate decarboxylases (PDC)

- acetyltransferase (HSCoA)

Factors influencing on enzyme activity

Effect of temperature

The optimum of temperature is that temperature at which the activity of enzyme is maximal. For most enzymes optimal temperature is within the range from +35C to +45C. if the temperature is below than optimal one so that is called reversible innactivation of enzymes. In this case the increase of temperature to optimal one leads to the reactivation of enzymes. If the temperature is above than optimal one so that is called irreversible innactivation. In this case the increase of temperature above optimal one leads to the denaturation of enzymes and if decrease the temperature reactivation of enzymes isn’t observed.

The effect of pH on enzyme activity

The pH influences on the charge of active site of enzyme. The function of enzyme depends on the charge of active site. Optimal pH is pH of environment at which the activity of enzymes is maximal.

For most enzymes the optimal pH is within the range 4-7 (e.g. alfa-amylase has opt.pH 6.8). But there are exception. For example, enzyme pepsin has optimal pH 1.5-2.0; trypsin – 8.0-9.0.

The effect of enzyme concentration

Increase of enzyme concentration increases the enzymic activity (directly proportional relationship)

<== попередня сторінка	\|	наступна сторінка ==>
Specificity	\|	The effect of substrate concentration

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