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20 Cards in this Set

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  • Back
At high [S], all E is ES so...
-plateu is due to satuaration effect
-units: uM/min
-observed when virtually all E is present as ES complex
-max rate, extrapolate to at high [S]
-record it per active site of E
-turnover number
-units: sec-1
-describes the limiting rate of an enzyme (catalytic rxn at satuaration)
-concentration of S converted to P per unit time per enzyme site
-at high [S], reaction is independent of [S] b/c all E sites are filled
Reach at which [S]=km
-km is the substrate concentration that provides one-half the maximal rate
-it's [S] that provides 1/2 the rate
-50% of the sites are occupied by substrate (1/2 the rate)
Consider [S] <<<<< Km
-v is dependent upon substrate concentration and enzyme concentration
-v is dependent upon formation of ES -> P
-initial region where if double [S], rate doubles
-linear region
Specificity constant
Kcat/Km (uM-1sec-1)
-use to compare enzymes
-predicts how efficient enzyme is at binding S and going forward to P
-at extrememy E, it predicts the probability of forming a product (ES -> P)
Designing an experiment regarding enzyme kinetics
-take into account assumptions of steady state
Experiment 1: [E] is very low relative to [S]
-goal: measure initial period of reaction where P formation is linear
-slope provides the rate K or V or Vo
-units: uM product produced per unit time (uM/s or uM x s-1)
Experiment 2: function of [S]
-increase [S]
-family of lines
-report as uM x s-1 or s-1
-remember, low [S] have dramatic increase of rate with additional [S] (below slope line see this)
High [S]
-Km has no role when all E sites are satuarated
-slowest step (k+2) determines rate (rate limiting step)
-Km is the [S] that provides 1/2 Kcat or Vmax
-50% sites ES/50% Efree
[S] <<<<<<< Km
-rate is directly proportional to [S]
-rate is linear
-slope = Kcat/Km (uM-1s-1)
-Kcat tells how fast can go when all sites are satuarated
-Km predicts affinity of S for E
units: uM⁻1s⁻1
-predicts lower limit of K₊₁
-higher number means better substrate since it is lower limit predicotr
-higher # = weaker binding
-E colliding with S
-concentration dependence
units: uM-1 s-1
K₋₁ and K₊₂
units: s-1
-exponential functions
-concentration has nothing to do w/ ES ->P or ES backwards
3 steady state parameters
Kcat: s-1, turnover numerb
Km: uM, SS dissociation constant
Kcat/Km: uM-1s-1, specificity constant
Are there enzymes that do not obey M-M kinetics?
-yes, when have evidence of cooperativity or allosteric regulation
-look for sigmoidal behavior
-may not be able to detect sigmoidal behavior at the conditions of the expt.
Linear Transformation of kinetic data
-Lineweaver-Burk double reciprocal plot
-Eadie-Hofstee plot(v vs. v/[S])
-Hanes-Woolf plot([S]/v vs. [S])
-used more often
-using really only low [S] data
Weaknesses of Lineweaver-Burk
-data the most difficult to obtain techinically (low[S]) given most weight in determining linear fit
-difficult to evaluate quality of data directly (scatter, satuaration)
-cannot determine Kcat (Vmax) or Km directly from the plot