BCH 380 1st Edition Lecture 12 Outline of Last Lecture II. MyoglobinA. Structure and locationIII. HemoglobinIV. HemeOutline of Current Lecture V. Properties of EnzymesVI. Kinetic Experiments Current LectureChapter 5 – Properties of EnzymesWhat are Enzymes?- Enzymes are catalysts- They catalyze biological reactions, i.e. they increase the rate at which biological reactantsare converted into products by a factor of 10^3 to 10^20. Example of an oxidoreductase: Lactate is oxidized to pyruvate, while NAD+ is reduced to NADH. This reaction is catalyzed by the enzyme Lactate Dehydrogenase.Example of a Transferase: The amino group is transferred from alanine to apha-ketoglutarate Example of hydrolase: The pyrophosphate bond is hydrolysed to produce two moles of phosphate per mole of pyrophosphate. Example of a lyase: Lyases catalyze lysis of a substrate, generating a double bond in the process. These are nonhydrolytic, nonoxidative elimination reactions. In the reverse direction, they are called synthase, which catalyze the addition of one substrateExample of an isomerase: Isomerases catalyze structural change within a single molecule (isomerization reactions).Example of a ligase: Ligases catalyze ligation, or joining of two substrates. These reactions require the input of the chemical energy of a nucleotide triphosphate such as ATP. Kinetic Experiments - Rate of a simple chemical reaction:(Reveal Enzyme Properties)- The amount of product produced over time (∆P/∆t = v) is plotted for several different initial substrate concentrations. - The initial velocity (V0) is the slope of the progress curve at the beginning of the reaction- The velocity clearly varies with the substrate concentration, [S], i.e. V0 depends on [s]- Vo=k[S]Consider an enzyme catalyzed reaction that converts Substrate to Product, S to PE + S  ES  E + P- This reaction takes place in two distinct steps- First the enzyme binds the substrate to form an enzyme-substrate complex- Then the actual chemical reaction occurs with dissociation of the product- Thus, the rate depends on the overall concentrations of S and PIn enzyme kinetics, k2 is also referred as kcat-The velocity measured during this short period is the initial velocity, Vo-The equation for a rectangular hyperbola is: y=ax/(b+x), where a is a asymptote of the curve, i.e. Vmax and b is the point on the x axis corresponding to the value of a/2In enzyme kinetics, y=Vo, x=[S], a =Vmax, while b=”Km”, also known as the Michaelis constantThe complete equation is: Vo = (Vmax[S])/(Km+[S])The lower the value of Km, the more tightly substrate is bound (higher affinity)- Km is a measure of the affinity of the enzyme for the substrateKcat is the rate constant for conversion of the ES complex to E+P.Vmax=Kcat[E]totalThus, Kcat =Vmax/[E]totalCatalase: 2H2O  2H2O + O2 Catalytic Proficiency = (Enzymatic Rate Constant)/(Nonenzymatic Rate