Problem Set 5 - Questions PDF

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BIOC*2580* Problem*Set*5:*Enzyme*rates( ( 1. Trypsin(catalyses(the( hydrolysis(of(3.3(μmol(of( peptide(substrate(in(5(minutes(when(2.0(μg( of( trypsin( is( present( in( 3( mL.( ( Calculate( the( rate( of( reaction,( enzyme( activity( and( specific( activity.( ( If(the(molar(mass(of(trypsin(is(25(kDa,(calculate(the(turnover(number.( ( 2. The(enzyme(catalase(hydrolyses(the(breakdown(of(hydrogen(peroxide,(H2O2.((If(the(turnover( number(for(catalase(is(5.0(x(105(s,1,(and(the(molar(mass(of(catalase(is(240(kDa,(calculate(the( specific( activity( of( catalase( in( mol( min,1( mg,1.( ( If( 1.0( mg( of( catalase( is( added( to( 1( L( of( hydrogen(peroxide,(determine(the(rate(of(reaction.( ( 3. An(extract(of(E.#coli# containing(all(the(soluble(enzymes(present(in(the(bacteria(was(assayed( for( phosphatase( activity( (an( enzyme( that( hydrolyses( phosphate( esters),( giving( a( value( of( 0.30(μmol(hydrolysed(per(minute(per(mg(of(total(protein.(After(purification(of(the(enzyme,( the( specific( activity( was( again( measured,( and( was( found( to( be( 0.96( μmol( hydrolysis( per( minute(per(μg(of(the(pure(enzyme.( (Suggest(a(reason(for(the(apparent(difference(in(specific( activity.(What(%(of(all(the(proteins(found(in(E.#coli(is(made(up(by(phosphatase?( ( 4. Indicate(whether(the(following(statements(are(true(or(false.((If(false,(try(to(explain(why.( ( a) The( initial( rate( of( an( enzyme,catalyzed( reaction( is( independent( of( substrate( concentration( b) At( saturating( levels( of( substrate,( the( rate( of( an( enzyme,catalyzed( reaction( is( proportional(to(substrate(concentration( c) The(Michaelis(constant(KM(is(equal(to(the(substrate(concentration(at(which(v(=(1/2(Vmax( d) The(KM(for(an(enzyme(varies(with(enzyme(concentration([E]t( e) The(KM(for(an(enzyme(varies(as(a(function(of(inhibitor(concentration( f) KM(=(1/2(Vmax( ( 5. Calculate(the(rate(of(reaction(catalyzed(by(an(enzyme(with(KM(=(2.5(x(10,4(mol(L,1(and(Vmax(=( 2.0(x(10,6(mol(L,1(s,1,(for(substrate(concentrations(of(1.0(x(10,4,(2.5(x(10,4,(0.5(x(10,4(and(1.0(x( 10,3(mol(L,1.( ( ( Why(does(KM(have(units(of(concentration?( ( 6. The(KM(for(an(enzyme(is(1.0(x(10,5( mol(L,1.((At(a(substrate(concentration(of(0.01(mol(L,1,(the( rate(of(reaction(is(37(μmol(min,1.((A(similar(result(is(obtained(at(a(substrate(concentration(of( 0.001(mol(L,1.((What(is(going(on?( ( 7. Calculate( vo/Vmax( for( the( following( values( of( [S]/KM:( 0.01;( 0.1;( 0.25;( 0.5;( 1.0;( 2.0;( 4.0;( 10;( 100.(

Problem(set(5(,(page(1(

( 8. Calculate( values( of( [S]/KM( that( give( vo/Vmax( values( of( 0.10,( 0.125,( 0.333,( 0.5,( 0.667,( 0.80,( 0.90,(0.99.( ( 9. You(have(just(enough(enzyme(to(carry(out(exactly(six(determinations(of(rate(for(an(enzyme( with(unknown(Vmax(and(KM.((What(substrate(concentrations(would(you(use(to(get(the(most( information(about(the(enzyme,(if(the(supply(of(substrate(is(unlimited?(((Hint:(most(enzymes( have(KM(values(between(10,6(and(10,3(M)( ( 10. How(is(the(turnover(number(of(an(enzyme(related(to(k2?((How(is(it(related(to(Vmax?( (

A(binding(equilibrium(constant(Ks(can(be(defined(for(the(process((E(+(S(

(

So,( K s =

k [ES ] = 1 ( [ E][ S ] k −1

(ES(

What(is(the(relationship(between(KM(and(Ks?(

Problem(set(5(,(page(2(...