Untersuchungen zur Reaktion der Alkoholdehydrogenase mit Tritium-markierten Substraten

1966 ◽  
Vol 21 (6) ◽  
pp. 540-546 ◽  
Author(s):  
Dieter Palm
Keyword(s):  
Alcohol Dehydrogenase ◽  
Temperature Dependence ◽  
Isotope Effect ◽  
Substrate Binding ◽  
Isotope Effects ◽  
Direct Interaction ◽  
Enzyme Complex ◽  
Temperature Range ◽  
Yeast Alcohol Dehydrogenase ◽  
Rate Controlling Step

Unexpectedly, the isotope effect of ethanol-1-Τ as a substrate of yeast alcohol dehydrogenase, increases with rising temperature from kH/kT = 3.2 at 5 —15°C to 3.8—4.7 at 20 —35 °C. This suggests a change of the rate controlling step as proposed by MÜLLER-HILL and WALLENFELS, who investigated the temperature dependence of the activation energies in this temperature range. A comparison of the affinities of propanol and butanol with the isotope effects of the corresponding tritium labelled compounds (propanol-1-Τ 6.7 at 25 °C, butanol-1-Τ 6.8 at 25 °C) supports the proposal, that during substrate binding, there must be a direct interaction between the enzyme complex and hydrogen which is removed in the reaction. These influences are less pronounced for the ethanol homologues which are bound less tightly to the enzyme. Therefore the H transfering step proper gives a greater contribution to the overall experimental isotope effect.

THE HYDROGEN ISOTOPE EFFECTS IN THE PYROLYSIS OF ETHYL-1,1,2,2-d4 BROMIDE AND OF ETHYL-d5 BROMIDE

1962 ◽  
Vol 40 (8) ◽  
pp. 1533-1539 ◽  
Author(s):  
Arthur T. Blades ◽  
P. W. Gilderson ◽  
M. G. H. Wallbridge
Keyword(s):  
Isotope Effect ◽  
Rate Constant ◽  
Hydrogen Isotope ◽  
Relative Rate ◽  
Isotope Effects ◽  
Side Reaction ◽  
Relative Rate Constant ◽  
Temperature Range ◽  
Rate Controlling Step ◽  
Constant Expression

The relative rate constant expression has been obtained for the decomposition of ethyl-1,1,2,2-d4 bromide under inhibiting conditions in the temperature range 697.6 to 999.1 °K,[Formula: see text]The pressure dependence of the isotope effect has been investigated both with and without inhibitor, and in each case it has been shown that the isotope effect increases with decreasing pressure.The relative rate constant expression for the ethyl-h5, ethyl-d5 bromide comparison was also obtained in the temperature range 730.9 to 964.8 °K,[Formula: see text]The isotope effect is again pressure dependent, falling to lower values as the pressure is decreased.The data are used to demonstrate that the inhibited decomposition of ethyl bromide is primarily a molecular process, and that the rate-controlling step involves a carbon–hydrogen bond break.A side reaction that produces small amounts of ethane has been observed.

Untersuchungen zur Reaktion der Alkoholdehydrogenase mit Tritium -markierten Substraten

1966 ◽  
Vol 21 (6) ◽  
pp. 547-551 ◽  
Author(s):  
Dieter Palm
Keyword(s):  
Alcohol Dehydrogenase ◽  
Isotope Effect ◽  
Isotope Fractionation ◽  
Kinetic Isotope Effect ◽  
Retention Volume ◽  
Deae Cellulose ◽  
Yeast Alcohol Dehydrogenase ◽  
Kinetic Isotope ◽  
Direct Indication ◽  
Rate Controlling Step

The temperature dependence of the kinetic isotope effect of NADH-T in the acetaldehyde reduction by yeast alcohol dehydrogenase showed a discontinuity which can be explained by a change of the rate controlling step. The magnitude of the isotope effect is largely dependent on the nature of the unlabelled aldehyde and increases in the order acetaldehyde, propionaldehyde, butyraldehyde. This is a direct indication that the second substrate influences the nature of the H-transfer from NADH. During substrate binding the aldehyde causes an effect on the transferable H of NADH. This effect is less pronounced for the less effective substrates propionaldehyde and butyraldehyde. Comparing the homologue aldehydes the small size of the isotope effect gives an indication that acetaldehyde is the natural substrate of yeast alcohol dehydrogenase.The purification of NADH-T on DEAE-Cellulose is connected with isotope fractionation which amounts to 0.4 — 1.1% of retention volume.

DEUTERIUM KINETIC ISOTOPE EFFECTS: V TEMPERATURE DEPENDENCE OF β-DEUTERIUM EFFECTS IN WATER SOLVOLYSIS OF ISOPROPYL COMPOUNDS

1961 ◽  
Vol 39 (10) ◽  
pp. 1989-1994 ◽  
Author(s):  
K. T. Leffek ◽  
R. E. Robertson ◽  
S. E. Sugamori
Keyword(s):  
Temperature Dependence ◽  
Isotope Effect ◽  
Isotope Effects ◽  
Zero Point ◽  
Kinetic Isotope Effects ◽  
Methyl Groups ◽  
Deuterium Isotope Effect ◽  
Point Energy ◽  
Kinetic Isotope ◽  
Enthalpy Of Activation

The secondary β-deuterium isotope effect (kH/kD) has been measured over a range of temperature for the water solvolysis reactions of isopropyl methanesulphonate, p-toluenesulphonate, and bromide. In these cases the isotope effect is due to a difference in entropies of activation of the isotopic analogues rather than a difference in the enthalpies of activation. It is suggested that the observed isotope effect is due to internal rotational effects of the methyl groups in the isopropyl radical, and the lack of an isotope effect on the enthalpy of activation is accounted for by a cancellation of an effect from this source and one from zero-point energy.

Hydrolysis of α-bromoisobutyrate ion in water

1967 ◽  
Vol 45 (18) ◽  
pp. 2071-2077 ◽  
Author(s):  
B. N. Hendy ◽  
W. A. Redmond ◽  
R. E. Robertson
Keyword(s):  
Temperature Dependence ◽  
Isotope Effect ◽  
Deuterium Isotope Effect ◽  
Detailed Mechanism ◽  
Temperature Range ◽  
Rate Of Hydrolysis ◽  
Hydrolysis Of

The temperature dependence of the rate of hydrolysis of α-bromoisobutyrate ion in water was determined over a temperature range 9–37 °C. From these data corresponding values of ΔH≠, ΔS≠, and ΔCP≠ have been derived. The implication of these terms, together with corresponding data for hydrolysis in D2O and for the secondary deuterium isotope effect from the hydrolysis of (CD3)2CBrCOO−, provide a basis for reexamining the detailed mechanism with particular reference to accompanying solvent reorganization.

Untersuchungen zur Reaktion der Alkoholdehydrogenasen mit Tritium-markierten Substraten

1968 ◽  
Vol 23 (5) ◽  
pp. 623-628 ◽  
Author(s):  
Dieter Palm ◽  
Tankred Fiedler ◽  
Dorothea Ruhrseitz
Keyword(s):  
Alcohol Dehydrogenase ◽  
Isotope Effect ◽  
Isotope Effects ◽  
Ternary Complexes ◽  
Liver Alcohol Dehydrogenase

[1,1-T]-ethanol,:1,1-T]-propanol and [1,1-T]-butanol exhibit small isotope effects (kH/kT=1.3-1.8) in the liver alcohol dehydrogenase catalyzed reaction NAD® + alcohol ⇌aldehyde +NADH+H®. Presence of semicarbazide (with [1,1-T] -ethanol) or substrat inhibition (with [1,1-T] -butanol, 2.10-2-m.) raises the isotope effect (up to 4.1 at 25 °C) by introducing partial irreversibility to the interconversion step of the ternary complexes. This is in agreement with the Theorell-Chance mechanism as extended by DALZIEL. Thus, isotope effect determinations confirm both, the presence of ternary complexes and their kinetic insignificance for lower aliphatic substrates.The results are markedly different from analogous kinetics with the yeast enzyme.

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