Skip to main content

Renin Angiotensin Mechanism.

Regulation of Enzymes: enzyme induction and repression, allosteric enzymes regulation.

Introduction:

  • The regulation of enzyme reaction velocity is critical for the coordination of many metabolic processes. 

  • Because many substrates have intracellular levels in the range of the Km, the rates of most enzymes are responsive to changes in substrate concentration. 

  • As a result, an increase in substrate concentration causes an increase in reaction rate, which tends to return substrate concentration to normal. 

  • Furthermore, when physiologic conditions change, some enzymes with specialized regulatory functions respond to allosteric effectors and/or covalent modification, or their rates of enzyme synthesis (or degradation) change.

  • In this lecture we are going to study following mechanisms,

    • Induction and repression of enzyme synthesis.

    • Allosteric enzyme regulation.

  1. Induction and repression of enzyme synthesis:

  • Cells can also alter the speed of enzyme degradation or, more commonly, the rate of enzyme synthesis to control the amount of enzyme present.

  • The increase (induction) or decrease (repression) of enzyme synthesis changes the overall population of active sites.

  • Enzymes whose production is regulated are frequently ones that are only required during particular developmental stages or under particular physiological circumstances.

    • e.g.  increased levels of insulin as a result of high blood glucose levels cause an increase in the synthesis of enzymes associated with  glucose metabolism. 

  • Enzymes that are constantly in use, on the other hand, are usually not regulated by changing the rate of enzyme synthesis. 

  • Changes in enzyme levels as a result of protein synthesis induction or repression are slow (hours to days), compared to allosterically or covalently regulated changes in enzyme activity, which occur in seconds to minutes.

  1. Allosteric enzyme regulation.

  • Allosteric enzymes have a binding site other than the active site for effector molecules. 

  • The binding changes the catalytic properties of the enzyme because it changes its conformation. 

  • Effector molecules can be inhibitors or activators. 

  • A well-regulated biological system is present in all organisms. 

  • Various regulatory mechanisms operate in the body to monitor and adapt to changes in the inside and outside environment. 

  • Gene expression, cell division, hormone production, metabolism, and enzyme production are all regulated to ensure proper development and survival. 

  • Enzymes are regulated by allostery, in which binding at one site affects the binding at subsequent sites.

  • Properties

    • Biological catalysts speed up reactions through their action on enzymes.

    • The active site of allosteric enzymes, as well as the substrate-binding site, have additional sites. C-subunit refers to the substrate-binding site, and R-subunit or regulatory subunit refers to the effector binding site.

    • Allosteric sites can occur at more than one position on an enzyme molecule

    • They can respond to multiple conditions, which impact how they react biologically.

    • An effector is a binding molecule, which can be both inhibitory and activating

    • By binding an effector molecule to an enzyme, the enzyme's conformation is altered.

    • Enzymes that are activated increase their activities, while enzymes that are inhibited decrease their activities after they are bound.

    • S-curves are typical instead of hyperbolic curves for velocity vs substrate concentration graphs for allosteric enzymes.


Effects of negative  positive effectors on an allosteric enzyme. 

A. Vmax is altered. 

B. The substrate concentration that gives half-maximal velocity (K0.5) is altered.

  • Allosteric regulation can be divided into two types,

    • Homotropic regulation.

    • Heterotropic regulation.

  • Homotropic regulation - 

    • Substrate molecules can also act as effectors here. 

    • A major component of this process is the activation of enzymes, also known as cooperativity, i.e., oxygen binds to hemoglobin.

  • Heterotopic regulation - 

    • The substrate is not the same as the effector. Activators or inhibitors of the enzyme can be used, e.g., CO2 binding to hemoglobin.

  • The two types of allosteric regulation are inhibition and activation, based on the action of the regulator.

  • Allosteric inhibition - 

    • If a protein complex of an enzyme is bound to an inhibitor, the enzyme's activity decreases due to conformational changes at all the active sites.

  • Allosteric activation - 

    • Activators bind to active sites and increase their function, which in turn increases substrate binding.

Commonly Asked Question.

  1. Write in detail about Regulation of enzymes in the body.

 

Labels:

Popular posts from this blog

Heat Exchangers and Heat Interchangers.

  In pharmaceutical industries many types of equipments are used for transfer of heat, they can be classified as follows, Heat Exchangers. Heat Interchangers. Heat Exchangers: These devices are used for transferring heat from a fluid (Hot Gas or Steam) to another fluid (Liquid) through a metal wall. Heat Interchangers: These devices are used for transferring heat from a One liquid to another liquid or one gas to another gas through a metal wall. HEAT EXCHANGERS; The equipment used for heat transferring are known as heat exchangers. Some of the processes that involves heat transfer in pharmaceutical industries are: Preparation of starch paste (in steam jacketed kettle). Crystallization. Evaporation. Distillation.  Classification of heat exchangers On the basis of transfer of heat, heat exchangers are classified as: Direct transfer type:  The hot and cold fluids are separated by a metal wall through which the heat is transferred from hot fluid to cold fluid. E.g. shell and ...
Read more

Rate of Drying Curve.

  Definition Drying is defined as the removal of liquid from a product usually with application of heat. Rate of Drying Curve. Drying process can be divided into three periods Initial Adjustment Period. Constant drying rate period. First falling drying rate period. Second falling rate period. Initial Adjustment Period (A-B): Also called the “ Heating up” period . In this period the substance gets heat and increases in temperature. Drying has not yet started. Constant drying rate period (B-C): During this period the temperature of the solid and the rate of drying remain constant. The moisture evaporating from the surface is replaced by water diffusing from the interior of the solid at a rate equal t o the rate of evaporation.  The moisture content at the end of constant rate (point C) is referred to as the critical moisture content (CMC).  At CMC, dry spots start appearing and drying rate starts falling . First falling drying rate period (C-D): This period is also called ...
Read more

Glycogenesis.

  Definition: Biosynthesis of Glycogen from Glucose is called Glycogenesis. Glycogen is synthesized  Depending on the demand for glucose and ATP (energy), insulin promotes the glucose conversion into glycogen. Glycogen is the major storage form of carbohydrate in animals similar to starch in plants. It is a homopolymer made up of repeated units of α- D glucose and each molecule is linked to another by 1→4 glycosidic bonds . Once there is a chain consisting of 8 to 10 glycosidic residues in the glycogen fragment, branching begins by 1→6 linkages . Glycogen is stored in liver and skeletal muscles. Location: Cytoplasm of cells in the muscle, liver, and adipose tissue. Steps Involved in Glycogenesis: Glucose is converted into glucose-6-phosphate by the action of glucokinase or hexokinase  with conversion of ATP to ADP. Glucose-6-phosphate is converted into glucose-1-phosphate by the action of phosphoglucomutase. Glucose-1-phosphate is converted into UDP-glucose by the actio...
Read more