Hyperbolic mixed, predominantly catalytic inhibition
- Km↓ The apparent Michaelis constant decreases with increasing [X]
- V ↓ (∴kcat ↓) The apparent limiting rate, and therefore the catalytic constant, decrease with increasing [X]
These symbols are shown only when the featured dependencies of the parameters on modifier concentration have been demonstrated by the authors.
|EC no.||Modifier||Substrate(1)||Name given by authors (2)||Reference(3)|
|188.8.131.52||Arsenite||ABTS (4)||Mixed with preference toward uncompetitive inhibition|
Km↓, V↓, KX = 2.3 mM
|2||Glycerol kinase (5)|
|184.108.40.206||IIAGlc (6)||MgATP||K-type activation & V-type inhibition, Km↓, V↓|
α = 0.5, β = 0.12, KX = 1.3 μM
|3||Glycerol kinase (7)|
|220.127.116.11||IIAGlc (6)||MgATP||K-type activation & V-type inhibition, Km↓, V↓|
α = 0.25, β = 0.13, KX = 8 μM
|4||'Cytochrome P450' (8)|
|—(8)||p-Nitrobenzoate||Zoxazolamine||S, I-hyperbolic noncompetitive (9)||Sternson
|5||Coagulation factor IXa (FIXa)|
|18.104.22.168||Nitrophorin-2 ||S-2765, mix (a) (11)||Hyperbolic mixed-type inhibition, Km↓, V↓|
α = 0.56, β = 0.19, KX = 15.5 nM
|6||Coagulation factor IXa (FIXa)|
|22.214.171.124||Nitrophorin-2 ||S-2765, mix (b) (11)||Hyperbolic mixed-type inhibition, Km↓, V↓|
α = 0.23, β = 0.14, KX = 16.5 nM
|7||Coagulation factor IXa (FIXa)|
|126.96.36.199||Nitrophorin-2 ||S-2765, mix (c) (11)||Hyperbolic mixed-type inhibition, Km↓, V↓|
α = 0.12, β = 0.023, KX = 23.3 nM
|8||Coagulation factor IXa (FIXa)|
|188.8.131.52||Nitrophorin-2 ||S-2765, mix (d) (11)||Hyperbolic mixed-type inhibition, Km↓, V↓|
α = 0.07, β = 0.035, KX = 12.6 nM
|9||Coagulation factor IXa (FIXa)|
|184.108.40.206||Nitrophorin-2 ||S-2765, mix (e) (11)||Hyperbolic mixed-type inhibition, Km↓, V↓|
α = 0.57, β = 0.21, KX = 21.6 nM
|220.127.116.11||Compound 9||Acetylthiocholine||Hyperbolic mixed-type inhibition|
α = 0.7, β = 0.08, KX = 1.6 μM
|18.104.22.168||Compound 10||Acetylthiocholine||Hyperbolic mixed-type inhibition|
α = 0.47, β = 0.24, KX = 2.1 μM
|22.214.171.124||Compound 39||Acetylthiocholine||Mixed-type inhibition with pronounced uncompetitive character|
α = 0.33, β = 0.05, KX = 0.66 μM
|126.96.36.199||Compound 40||Acetylthiocholine||Mixed-type inhibition with pronounced uncompetitive character|
α = 0.37, β = 0.08, KX = 1.7 μM
|188.8.131.52||Cherry-NbVIM_38 (12)||Cephalothin (13)||Mixed, predominantly uncompetitive inhibition|
α = 0.6, β = 0.4, KX = 9 μM
|184.108.40.206||Chloride anion, Cl–||L-Dopa||Reversible partial hyperbolic uncompetitive (14)||Park
pH = 4.3
|220.127.116.11||p -Mercaptobenzoic acid-coated|
|Hyperbolic mixed inhibition with predominantly uncompetitive character|
α = 0.43, β = 0.33, KX = 21 nM
|18||Dipeptidyl-peptidase I (monomer)|
|18.104.22.168||3'-Nitrophthalanilic acid||H-Gly-Phe-7-amino-4-methylcoumarylamide||Hyperbolic mixed inhibition|
α = 0.40, β = 0.26, KX = 560 μM
|22.214.171.124||Dromedary antibody variable domain fragment (VHH 1589)||p-nitrophenyl riboside||Hyperbolic mixed inhibition|
α = 0.76, β = 0.46, KX = 67 nM
(1) Always the varied substrate. In two- or more-substrate reactions the concentration(s) of the non varied substrate(s) is/are kept constant.
(2) Name of the mechanism given by the authors in the quoted reference. α, β and the inhibition/activation constants for the modifier (X), uniformly denoted KX, are the values specified by the authors. In some cases, missing parameters have been calculated from graphical or tabular data provided in the papers. In two- or more-substrate reactions, KX represents an apparent constant at given concentrations of the fixed substrates and no calculations of the intrinsic values have been attempted.
(3) Full references at the end of the page provide also the digital object identifier (doi), if available. Clicking the authors (highlighted) opens the reference in PubMed.
(4) ABTS = 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid).
(5) With the amino acid substitution E478C.
(6) IIAGlc Glucose-specific phosphocarrier protein of the phosphoenolpyruvate:glycose phosphotransferase.
(7) With the amino acid substitution E478C, T428V and R429N.
(8) Enzyme activity in rat liver microsomes called ‘Zoxazolamine oxidase, possibly the Unspecific monooxygenase, EC 126.96.36.199. Zoxazolamine = 5-Chloro-1,3-benzoxazol-2-amine, a muscle relaxant now dismissed due to hepatotoxycity.
(9) The mechanism can be clearly diagnosed from Figure 1. However, a very personal definition of the parameters in Table I and just straight lines shown without experimental points in Figure 1A hamper the calculation of kinetic parameters.
(10) Nitrophorin-2 = ferriheme protein from the insect Rhodnius prolixus.
(11) S-2765 = N-α-benzyloxycarbonyl-D-arginyl-glycyl-arginyl-p-nitroanilide was the substrate for monitoring the generation of FXa from FX after activation by FIXa. The inhibition parameters were measured with different reaction mixtures that included, besides catalyst, substrate, inhibitor, an artificial membrane surface consisting of a mixture of L-α-phosphatidyl-L-serine (PS) and L-α-dioleoylphosphatidylcholine (PC), and FVIIIa. Either the surface or FVIIIa or both together were necessary for the inhibitory action. In all of following combinations the mechanism HMx(Sp<Ca)I was observed:
- mix (a) = PS/PC alone: FIXa (10 nM), PS/PC (20 μM), FX (10-300 nM)
- mix (b) = PS/PC + FVIIIa: FIXa (0.25 nM), PS/PC (0.5 μM), FVIIIa (15 U/mL), FX (5-150 nM)
- mix (c) = platelets alone: FIXa (10 nM), platelets (1 × 108/mL), FX (10-300 nM)
- mix (d) = platelets + FVIIIa: FIXa (0.25 nM), platelets (5 × 107/mL), FVIIIa (15 U/mL), FX (5-150 nM)
- mix (e) = FVIIIa alone: FIXa (10 nM), FVIIIa (30 U/mL), FX (10-400 nM)
(12) Cherry-NbVIM_38 = single-domain antibody fragment (camelid nanobody) against the clinically-relevant Verona integron-encoded metallo-β-lactamase. In addition to the inhibition by the nanobody, Sohier et al. (2013) also describe substrate inhibition due to compulsory addition of a second substrate molecule to the ESX complex: ESX + S ⇄ SESX.
(13) A first-generation cephalosporin antibiotic.
(14) According to Fig. 4B in (Park, 2005), the mechanism described is HMx(Sp<Ca)I. The confusion about uncompetitive interactions in this and other publications is due to misinterpretation of the basic mechanism as discussed elsewhere (pp. 150-153 and 273-276).
(15) At pH = 7.4 the mechanism changes from inhibition to activation with mechanism HCaA.
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