Chemistry Labs

Biochemistry and biomedical chemistry

Enzymes and enzyme kinetics

Enzymes accelerate reactions by lowering the activation free-energy barrier; they do not change the equilibrium constant.

1 Lower secondary2 Upper secondary3 Undergraduate4 Advanced5 Research

IntuitionIntuition: the central idea

Enzymes accelerate reactions by lowering the activation free-energy barrier; they do not change the equilibrium constant.

Explore the schematic model; it illustrates a concept rather than replacing experimental evidence.

SchoolSchool level: key concepts and a first application

Definition: Core concept

For a simple one-substrate enzyme at initial rate, the Michaelis–Menten model gives a hyperbolic dependence on substrate concentration.

The enzyme–substrate complex ES forms by binding; the enzyme then converts substrate to product. In the simplest steady-state picture ES reaches a quasi-constant concentration while product accumulates.

Key terms and meaning
TermInterpretation
KmSubstrate concentration at half-maximal initial rate.
VmaxUpper limiting rate when substrate saturates the enzyme.
InhibitionReduction of activity by molecules that affect binding or catalysis.

Example: Apply the idea

An enzyme has Vmax=12V_{max}=12 μmol min⁻¹ and KM=3K_M=3 mM. Estimate v0v_0 at [S]=3[S]=3 mM.

Solution

Substitution gives v0=Vmax/2=6v_0=V_{max}/2=6 μmol min⁻¹. KMK_M is the substrate concentration at half-maximal rate in this model, not generally a binding dissociation constant.

UndergraduateUniversity level: quantitative description

v0=Vmax⁡[S]KM+[S]v_0=\frac{V_{\max}[S]}{K_M+[S]}

At [S]=KM[S]=K_M, v0=Vmax/2v_0=V_{max}/2; at [S]≫KM[S]\gg K_M the enzyme approaches saturation. Lineweaver–Burk linearization is historically useful but weights low-substrate points poorly.

References