Reading & Problems: LNC p. 207-212; p. 239 prob. 9a,b, 10; Segel p. 319 prob. 6,7, p. 321, prob. 15,16,19 (except "Z")
- Solve only for [S]>>Km, and for [S]<<Km.
For [S]>>Km, V = Vmax (zero order for [S]), and [P]t = Vmax•t,
[S]t =[S]0 - [P]t
For [S]<<Km, V = Vmax/Km•[S] (first order for [S]) and
- Rate of synthesis, and
- Rate of degredation
- Irreversible inhibitors - irreversibly bind to and inhibit the enzyme. Examples include DIFP and TPCK as inhibitors of chymotrypsin. They are covalently bound and do not dissociate from the enzyme.
- Reversible inhibitors - bind and release, the amount of inhibitor bound is determined by the concentration of inhibitor and its binding constant (Ki). Reversible inhibitors are important regulators of enzyme activity in cells.
B. Noncompetitive inhibitor - can bind whether or not substrate bound, prevents reaction when bound.
Some take home information:
|Inhibitor||Binds to||Constant changed|
|Noncompetitive||ES, E||Vmax lower|
|Uncompetitive||ES||Vmax lower, Km lower|
If constant is Higher -> multiple by "the inhibitor factor" = 1+([I]/KI)
If constant is Lower -> divide by "the inhibitor factor" = 1+([I]/KI)
Charles S. Gasser (Department of Molecular & Cellular Biology; UC Davis)