What changed: Km or Vmax?
Topic: Enzymes & kinetics
A student measures the initial rate of a purified bacterial phosphatase at many substrate concentrations, always assayed at 37 °C and the enzyme's optimal pH, and fits Michaelis–Menten curves to get Vmax and the apparent Km (the substrate concentration giving half the observed Vmax). Each treatment below is compared with the untreated enzyme at the same total enzyme concentration, unless stated. Inhibitors are used at one fixed concentration.
For each treatment, predict how the apparent Km, the Vmax, and the rate at a very low substrate concentration (far below Km) compare with the untreated enzyme.
Competitive inhibitor added
Apparent KmVmaxRate at very low [S]Pure noncompetitive inhibitor added
Apparent KmVmaxRate at very low [S]Uncompetitive inhibitor added (binds only the enzyme–substrate complex)
Apparent KmVmaxRate at very low [S]Twice as much enzyme in the assay
Apparent KmVmaxRate at very low [S]Enzyme pre-heated to 70 °C for 10 min (half the molecules unfold for good; the rest are undamaged), cooled, then assayed at 37 °C
Apparent KmVmaxRate at very low [S]Enzyme stored at 4 °C overnight, then warmed and assayed at 37 °C
Apparent KmVmaxRate at very low [S]
| Row | Apparent Km | Vmax | Rate at very low [S] |
|---|---|---|---|
| Competitive inhibitor added | |||
| Pure noncompetitive inhibitor added | |||
| Uncompetitive inhibitor added (binds only the enzyme–substrate complex) | |||
| Twice as much enzyme in the assay | |||
| Enzyme pre-heated to 70 °C for 10 min (half the molecules unfold for good; the rest are undamaged), cooled, then assayed at 37 °C | |||
| Enzyme stored at 4 °C overnight, then warmed and assayed at 37 °C |
Answer every part to submit.