Welcome to BTE 417 Presentation On Regulatory Enzymes

Zubaida Marufee Islam Lecture Mathematics and Natural Science Department BRAC University Presented by: Kabirul Islam Kanon – Asif Jahan Shuvro Presented to:

What are regulatory enzymes? A regulatory enzyme is an enzyme in a biochemical pathway which, through its responses to the presence of certain other biomolecules, regulates the pathway activity. This is usually done for pathways whose products may be needed in different amounts at different times, such as hormone production. Some examples are:  Aspartate transcarbamoylase  Pyruvate dehydrogenase kinase  Phosphofructokinase

Regulatory enzymes A A B C D E1 E2 E3 KEY ENZYME Rate limiting enzyme REGULATORY ENZYME (Catalyze the first step unique to particular pathway Regulatory enzyme adjust the overall rate of the pathway to meet the cell‘s demand Rate limited step Committed step (conversion of B to C) Usually irreversible

Enzyme Regulation ????? Enzyme regulation - is the control of the rate of a reaction catalyzed by an enzyme by some effector (e.g., inhibitors or activators) or by alteration of some condition (e.g., pH or ionic strength). Regulate – to control or direct according to a rule, principle or law

Enzyme regulation  Constitutive enzymes: Enzymes needed at the same level all of the time  Regulated enzymes: Enzymes needed under some conditions but not others For example enzymes of the Lac Operon Enzymes are made to break down lactose only if lactose is present

2 Types of Regulation Regulation of amount of enzyme made : At the level of transcription = is RNA made? At the level of translation = is protein made? Regulation of enzyme activity: Allosteric regulation Covalent modification Isoenzymes Proteolytic cleavage of proenzyme Slower process (minutes) Very rapid process (seconds or less than a second)

Allosteric Regulation: Allosteric enzymes have 2 binding site: 1-Active site binds substrate 2-Allosteric site (Effectors or modifiers) Binding of regulatory molecule to Allosteric site.It induce a conformational change in the enzyme Increase the enzyme activity(positive allosteric modifier/ activator ) Inhibit the enzyme activity(negative allosteric modifier/ inducer)

PFK-1 catalyzes an early step in glycolysis Phosphoenol pyruvate (PEP), an intermediate near the end of the pathway is an allosteric inhibitor of PFK-1 Example of allosteric enzyme - phosphofructokinase- 1 (PFK-1) PEP

Covalent Modification: Certain chemical groups are covalently linked to regulatory enzymes in a reversible manner to change their activity by changing their conformation.

Phosphorylation /dephosphorylation most common covalent modification involve protein kinases/phosphatase PDK inactivated by phosphorylation Amino acids with –OH groups are targets for phosphorylation( usually serine, tyrosine or threonine) Phosphates are bulky (-) charged groups which effect conformation

Isoenzymes - multiple forms of an enzyme which differ in amino acid sequence but catalyze the same reaction Isoenzymes can differ in:  kinetics,  regulatory properties,  the form of coenzyme they prefer and  distribution in cell and tissues Isoenzymes are coded by different genes Isoenzymes (isozymes) Some metabolic processes are regulated by enzymes that exist in different molecular forms - isoenzymes

Isoenzymes are important for diagnosis of different diseases There are 5 Isozymes of LDG:  H 4 – heart  HM 3 –reticuloendothelial system  H 2 M 2 -lung  H 3 M – kidney, pancreas  M 4 – liver, muscle Lactate dehydrogenase – tetramer (four subunits) composed of two types of polypeptide chains, M and H Example: lactate dehydrogenase (LDG) Lactate + NAD + pyruvate + NADH + H +

Activation by proteolytic cleavage Many enzymes are synthesized as inactive precursors (zymogens) that are activated by proteolytic cleavage Proteolytic activation only occurs once in the life of an enzyme molecule Examples of specific proteolysis Digestive enzymes –Synthesized as zymogens in stomach and pancreas Blood clotting enzymes –Cascade of proteolytic activations Protein hormones –Proinsulin to insulin by removal of a peptide

Aspartate transcarbamoylase: Feedback inhibition Committed reaction CTP is structurally different from the substrate, but binds to the allosteric or regulatory site of ATCase. ATCase catalyzes the first step in biosynthesis of pyrimidine. CTP inhibits ATCase At low conc. of CTP, rate is high At high conc. of CTP, rate is low

Any question??