Medical brain notes 25

  ENZYMES Introduction All the enzymes are proteins and they are produced by the living cells. They act as biological catalysts. Enzymes catalyse and enhance the rate of biochemical reactions occuring in various vital processes like breathing, digestion, pumping of heart, formation of body tissues, contraction of muscles, transport of ions across the plasma membranes etc.So without enzymes there is no life. They are inactive at OoC and destroyed by moist heat at 100oC. The term enzyme was first used by Kuhne (1878) to designate these ‘biological catalysts’. Sumner and My Back (1950) have defined the enzymes as “Simple or combined proteins acting as specific catalysts”. They affect the life of an organism to such an extent that life has aptly called as an orderly function of enzymes. The substances on which the enzymes act are called as “Substrates”. Enzymes are highly specific in their action (i.e) an enzyme can act on a single or a small group of closely related substrates. During...

  Chemical nature of enzymes All the enzymes are proteins with no exception. Some enzymes are simple proteins i.e. their molecules consist of only amino acids. Many enzymes are conjugated proteins and their molecules consist of aminoacids and a non-protein part (not made up of amino acids). The non-protein part of the enzyme is known as coenzyme or prosthetic group, without which the enzyme is inactive. The protein part of the enzyme (in conjugated type) is known as the apoenzyme. The coenzyme and the apoenzyme complex is called as holoenzyme. Coenzyme + Apoenzyme - - > Holoenzyme For example, pyruvate decarboxylase is an enzyme which catalyses the decarboxylation of pyruvate to form acetaldehyde. The non-protein part of the enzyme is thiamine pyro phosphate without which the reaction can not be proceeded. The non-proteinaceous part is either loosely or tightly bound with the apoenzyme. If the coenzymes are tightly bound with the apoenzymes the coenzymes are called as prosthetic...

  Naming of enzymes Except the enzymes ptyalin, pepsin, trypsin and renin, all the other enzymes are usually named by adding suffix -  ase  to the main part of the name of the substrate on which they act. Examples : Maltase acts on maltose Lactase acts on lactose Lipases act on lipids Proteases act on proteins Amylases act on starch (amylum)

  Classification of enzymes The most comprehensive system for the classification of enzymes was devised in 1961 by the Enzyme Commission of International Union of Biochemistry (IUB). The 6 major classes of enzymes are   1. oxidoreductases Enzymes catalyzing oxidoreduction reactions between two substrates A and B are called as oxidoreductases In this reaction cytochrome C 1  is oxidised and cytochrome a is reduced simultaneously by the action of cytochrome C-oxidase. This class includes several subclasses based on the group on which the enzymes act. The enzymes acting on -CH -OH (1.1) -C=O (1.2) -C=CH (1.3) -CH-NH 2  (1.4) -CH-NH (1.5)   2. Transferases Enzymes catalysing the transfer of a group (x) from one substrate(AX ) to another are known as transferases. AX + B < - - > A’ + BX Example The reaction catalysed by alanine transaminase (ALT) is In this reaction the amino group from alanine is transferred to  α -ketoglutarate to form glutamate. These e...

  Factors influencing enzyme activity The activity of enzymes is markedly affected by several factors. These factors are 1. pH 2. temperature 3. substrate concentration 4. metal ions (activators) 5. inhibitors 6. enzyme concentration etc.   1. pH All the enzymes have a particular pH at which their activity is maximal; above or below this pH the activity is low. The pH at which the enzyme shows maximum activity is known as optimum pH. Some of the enzymes and their optimum pH are (a) Pepsin - 2.0                                                                                  ...