NEET UG 2005 — Botany Biomolecules

The catalytic efficiency of two different enzymes can be compared by comparing their $\mathrm{K}_{\mathrm{m}}$Km​ value or Michaelis Menten constant. The Michaelis constant is the substrate concentration at which the reaction rate is at half-maximum. The $\mathrm{K}_{\mathrm{m}}$Km​ describes the affinity of enzyme for a substrate molecule. Greater the affinity lower is the $\mathrm{K}_{\mathrm{m}}$Km​ value and sooner the $\mathrm{V}_{\max }$Vmax​ can be attained and vice versa. Related Theory $K_m$Km​ is the concentration of substrate which permits the enzyme to achieve half Vmax. An enzyme with a high $K_m$Km​ has a low affinity for its substrate, and requires a greater concentration of substrate to achieve Vmax. The relationship is defined by the MichaelisMenten equation: $$v=V_{\max } /\left(I+\left(K_m /[S]\right)\right)$$v=Vmax​/(I+(Km​/[S])) The Lineweaver-Burk double reciprocal plot rearranges the Michaelis-Menten equation as: $$1 / v=1 / V_{\max }+K_m / V_{\max } \times 1 /[S]$$1/v=1/Vmax​+Km​/Vmax​×1/[S] Plotting 1/v against 1/[S] give a straight line: where: $y$y intercept $=1 / V_{\max }$=1/Vmax​ gradient $=K_m / V_{\max }$=Km​/Vmax​ $x$x intercept $=-1 / K_m$=−1/Km​