enzymes, kinetics, inhibition

enzymes, kinetics, inhibition -...

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Unformatted text preview: !"#$%&" ( )*+,-". /0*"1#. 2*304015* )*+,-". !06" 7#&547$.8 "*+,-". 7#$ 90$3 :&"7$ .;""< 7*< ;&"#0.05*8 0*$"&7#1*: 90$3 .%4.$&7$" $5 =7#0>0$7$" #3"-0#7> $&7*.=5&-715* /", ?5*#";$. Enzymes are biological catalysts , very powerful and very speciFc. Enzymes increase rates of (bio)chemical reactions but have no effect on K eq (and no effect on overall G) of the reaction. Some enzymes need cofactors (inorganic ions or organic/metalloorganic coenzymes, derived from vitamins) for their catalytic activities. Different cofactors are useful for different kinds of chemical reactions, including transfers of speciFc kinds of groups or transfers of electrons. Kinetics : the study of reaction rates . Rates depend on rate constants. Rate constants depend inversely and exponentially on Arrhenius activation energy, G , the difference in free energy between free energy of transition state and free energy of reactant(s). Rate constants are increased by catalysts (enzymes), because enzymes decrease G . Enzymes lower G by affecting either H or S (or both). One way enzymes reduce G is by tight binding (noncovalent) of the transition state. Enzymes generally change the pathways by which reactions occur. Rate enhancement (factor by which enzyme increases the rate of a reaction) is determined by G , the decrease in G brought about by enzyme compared with uncatalyzed reaction's G . Reactions most often occur at the active site Models for enzyme-substrate binding are still evolving /", ?5*#";$. Kinetics is the study of reaction rates (velocities). Study of enzyme kinetics is useful for measuring concentration of an enzyme in a mixture (by its catalytic activity), its purity (speciFc activity), its catalytic efFciency and/or speciFcity for different substrates comparison of different forms of the same enzyme in different tissues or organisms, effects of inhibitors (which can give information about catalytic mechanism, structure of active site, potential therapeutic agents...) Dependence of velocity on [substrate] is described for many enzymes by the Michaelis-Menten equation kinetic parameters: Km (the Michaelis constant) kcat (the turnover number, which relates Vmax, the maximum velocity, to [Et], the total active site concentration) kcat/Km (the catalytic efFciency of the enzyme) can't be greater than limit imposed by diffusion control, ~108-109 M1sec1 Kinetic parameters can be determined graphically by measuring velocity of enzyme-catalyzed reaction at different concentrations of substrate (Vo vs. [substrate]). /", ?5*#";$....
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enzymes, kinetics, inhibition -...

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