Enzyme Regulation Notes

  • Focus of the video: regulation of enzyme activity; two general types of control are positive (stimulates activity) and negative (inhibits activity).
  • 10 ways to regulate enzyme activity covered; many operate via allosteric mechanisms, which are regulatory effects at sites other than the active site.
  • Key terminology is reinforced (substrate, enzyme, active site, regulatory site, allosteric, cooperativity, isozymes, PTMs, etc.).
  • Several concrete biological examples are provided to illustrate concepts (LDH isoforms, pyruvate dehydrogenase complex, Src kinase PTMs).
  • Abiotic factors (diffusion, pH, ionic strength, temperature) also modulate enzyme activity.
  • Asterisks indicate methods that can be implemented via allosteric regulation (except competitive inhibition, which is not allosteric per the lecture).

Note: Equations below are included to illustrate quantitative relationships for common regulatory scenarios.

  • Competitive inhibition can be described by the modified Michaelis–Menten form: V=V<em>max[S]K</em>m(1+[I]Ki)+[S]V = \frac{V<em>{max} [S]}{K</em>m\bigl(1+\frac{[I]}{K_i}\bigr) + [S]}
  • Noncompetitive inhibition (apparent Vmax change, Km unchanged): V=V<em>max/(1+[I]K</em>i)  [S]Km+[S]V = \frac{V<em>{max}/\bigl(1+\frac{[I]}{K</em>i}\bigr) \;[S]}{K_m + [S]}
  • For cooperativity (Hill equation): θ=[L]nKdn+[L]n\theta = \frac{[L]^n}{K_d^n + [L]^n} where n is the cooperativity coefficient.
  • Introduction to LDH isoforms can be summarized as combinatorial tetramer formation from M and H subunits: MMMM, MMMH, MMHH, MHHH, HHHH (five isozymes).
  • Basic idea of diffusion and temperature effects can be connected to rate constants via Arrhenius-type intuition: increasing temperature generally increases reaction rate constants but can disrupt protein folding if too high.