Enzymes O -CO -C Hi, Everybody!

Objectives Enzymes as Biological Catalysts The Properties of Enzymes Enzyme classification Substrate Binding and Enzyme Action Enzyme Inhibition Regulation of enzyme activity. Applications of Enzyme Action

Intended learning outcomes(ILO) State the different properties of enzymes.

Enzymes properties Enzymes properties 1-All enzymes are proteins 2-Enzymes do not determine the direction of reaction 3- Enzymes are highly specific 4-Some enzymes require cofactors

Ribozymes= Small group of catalytic RNA molecule which share in the posttranscriptional modification of nascent RNA.Ribozymes= Small group of catalytic RNA Pre-mRNA Mature mRNA Ribozyme Cleave phosphodiester bond of RNA 1-All enzymes are proteins except ribozymes

2-Enzymes do not determine the direction of reaction They only accelerate reaching the equilibrium state. The direction of the reaction is determined by the free energy change of the reaction=ΔG

3- Enzymes are highly specific TO their Substrate To the reaction 3-Enzymes are the most specific catalyst

Enzyme specificity

The enzyme is specific for one substrate e.g. glucokinase act only on glucose but not other hexoses. Urease acts on urea. Absolute specificity Enzymes Catalyze the same type of reaction on a number of structurally related substrates having the same type of bond. Hexokinase act on glucose, fructose, mannose Peptidase acts on peptide bonds in different proteins. Relative specificity Enzyme specificity

The enzyme is directing not only to the type of bond but also to the site of bond and the groups around it. Chemotrypsin acts on peptide bonds formed by certain amino acids Group specificity The enzyme are specific to the D- or to the L- isomer but not both. e.g. L-amino acid oxidase for L- amino acids not for D-AA. Stereospecificity Enzyme specificity

Specificity of Ser-Protease Family COO - C Asp COO - C Asp Active Site TrypsinChymotrypsinElastase cut at Lys, Argcut at Trp, Phe, Tyrcut at Ala, Gly Non-polar pocket Deep and negatively charged pocket Shallow and non-polar pocket O O –C–N–C–C–N– C NH 3 + O O –C–N–C–C–N– C O O –C–N–C–C–N– CH 3 Juang RH (2004) BCbasics

Some enzymes require a cofactor Let’s meet the team… Cofactors Metal ions (Mg, Fe, Cu) Coenzymes non protein, low molecular weight Usually derived from vitamins, heat stable Bind loosely with enzyme Few bind firmly(prothestic group) Regenerated after reaction

NON protein partcoenzymesMetal ion

NON protein part coenzymes Metal ion Metalloenzyme (tightly bound) Glutathione peroxidase contain Se Metal activated enzymes(loosely bound) Coagulation enzymes require Ca in blood

NON protein part coenzymes Tightly bound (Prosthetic group) Loosely bound, e.g. NAD Cofactors(metal)

NON protein part coenzymes Tightly bound (Prosthetic group) Covalently bound e.g. biotin, heme Non covalently bound e.g. FMN Loosely bound, e.g. NAD Cofactors(metal)

NON protein part coenzymes Tightly bound (Prosthetic group) Covalently bound e.g. biotin, heme Non covalently bound e.g. FMN Loosely bound, e.g. NAD Cofactors(metal) Metalloenzyme( tightly bound Glutathione peroxidase contain Se Metal activated enzymes(loosely bound) Coagulation enzymes require Ca in blood

Apoenzymes, coenzymes holoenzymes Let’s meet the team… Apoenzyme (protein part ) Coenzymes(non protein part) Holoenzyme (active catalytic unit)

Some enzymes require cofactors

Are specific non-protein organic or metallo-organic heat stable low molecular weight compounds required for the activity of the enzyme: Co-enzymes

Co-enzymes acts as Transient carrier of specific functional groups or atoms NAD carries the hydride ion during oxidation reduction reaction. Co-substrate(second substrate) Coenzymes has affinity for the enzyme similar to that of the substrate. The chemical changes in the coenzymes counterbalance those occurring in the substrate. If the substrate is oxidized, the coenzyme is reduced

The changes occurring in the coenzyme may more important than that occurring in the substrate. The reaction catalyzed by lactate dehydrogenase is mainly for oxidation of NADHH rather than reduction of pyruvate to lactate Co-enzymes

VitaminCo-enzymeFunction Thiamine ( B 1 ) TPP Oxidative decarboxylation Riboflavin (B 2 ) FAD, FMN Dehydrogenation Lipoic acid Oxidative decarboxylation Niacine NAD, NADP Dehydrogenation Pyrodoxine PLP Amino acid metabolism Biotin carboxylation reaction Pantothenic Acid CoA SH 1.Carobydrates,fat and lipids metabolism Folic Acid THF One carbon unit metabolism Co-enzymes derived from vitamins