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The effect of substrate concentration

The activity of enzymes is directly proportional to the substrate concentration. However, this is true only for a certain concentration after which the increase of its does not further increase the velocity of reaction. This phenomenon is named saturating concentration, i.e. all active sites are occupied by substrates and reaction doesn’t occur.

The influence of effectors

The effectors are divided into 2 groups: activators and inhibitors. Both of these groups have specific and non-specific representatives. For example, HCl (hydrochloric acid) is a specific activator for pepsin; ions of chlorine are specific activators for alfa-amylase; bile acids are specific activators for lipase of pancreas. Non-specific activators can activate many enzymes, e.g. ions of Mg are non-specific activators for phosphatases and kinases. Specific inhibitors are end-peptides of proenzymes. For example, pepsinogen is proenzyme (precursor of enzyme pepsin). It is activated by splitting off end-polypeptide under action of HCl. Such way is characteristically for most hydrolases of gaster and pancreas. For example, trypsinogen is activated by entherokinase (entheropeptidase) which splits off hexapeptide from its and trypsin is formed.

Non-specific inhibitors cause denaturation of enzyme, for example salts of heavy metals (copper sulfate etc).

Enzyme inhibition

There are competitive and non-competitive inhibition of enzymes. Beside of these 2 types of inhibition there are allosteric activation and inhibition of enzymes.

Competitive inhibition

This phenomenon occurs when inhibitor has structural resemblance with substrate. In this case inhibitor and substrate compete for binding with active site of enzyme. If the quantity of inhibitors more than substrate and complex enzyme-inhibitor is formed. For example, enzyme sucinate dehydrogenase. Its substrate is succinic acid and competitive inhibitors are malonic and oxaloacetic acids.

Enzyme glucose-6-phasphatase catalyzes the dephosphorylation of glucose-6-phosphate to glucose and phosphoric acid. glucose is competitive inhibitor. This is example of inhibition by products of reaction

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