scholarly journals 2H Kinetic Isotope Effects and pH Dependence of Catalysis as Mechanistic Probes of Rat Monoamine Oxidase A: Comparisons with the Human Enzyme

Biochemistry ◽  
2011 ◽  
Vol 50 (35) ◽  
pp. 7710-7717 ◽  
Author(s):  
Jin Wang ◽  
Dale E. Edmondson
Keyword(s):  
Monoamine Oxidase ◽  
Isotope Effects ◽  
Ph Dependence ◽  
Kinetic Isotope Effects ◽  
Monoamine Oxidase A ◽  
Kinetic Isotope ◽  
Human Enzyme

The pH dependence of xanthine oxidase catalysis in basic solution

1980 ◽  
Vol 58 (5) ◽  
pp. 394-398 ◽  
Author(s):  
John W. Bunting ◽  
Keith R. Laderoute ◽  
Donald J. Norris
Keyword(s):  
Xanthine Oxidase ◽  
Isotope Effects ◽  
Ph Dependence ◽  
Kinetic Isotope Effects ◽  
Similar Rate ◽  
Basic Solution ◽  
Kinetic Isotope ◽  
Steady State Kinetics ◽  
Pyridinium Cations ◽  
Kinetics Of

The steady-state kinetics of the oxidation of the following six heteroaromatic substrates by xanthine oxidase have been investigated over the range pH 9.0–11.1 at 25 °C, ionic strength 0.1: 1-methylquinolinium, 6-methoxy-1-methylquinolinium, 1-methylnicotinamide, 3-acetyl-1-methylpyridinium, and 1-(4-methoxyphenyl)pyridinium cations and 1-methylnicotinate zwitterion. For the first four of these species, kc and Km were evaluated as a function of pH while only kc/Km was accessible in the latter two cases. Where available, kc is pH independent, whereas plots of log (kc/Km) vs. pH are linear with slopes in the range 0.54–1.17.The rates of enzymic oxidation of the 1-methylquinolinium cation and its 2-deuterio derivative were investigated and kinetic isotope effects were calculated at pH 9.8 and 10.6: kcH/kcD = 1.7 and KmH/KmD = 0.4 at each pH. Detailed comparisons of the oxidation of heteroaromatic cations and xanthine-derived substrates indicate that similar rate-determining steps control the enzymic oxidations of these two classes of substrate.

Reactions of Muonium with simple biochemical solutes in water and micelles

1991 ◽  
Vol 69 (8) ◽  
pp. 1252-1258 ◽  
Author(s):  
Mary V. Barnabas ◽  
David C. Walker
Keyword(s):  
Reaction Mechanism ◽  
Organic Compounds ◽  
Rate Constants ◽  
Enhancement Factor ◽  
Isotope Effects ◽  
Ph Dependence ◽  
Kinetic Isotope Effects ◽  
Natural State ◽  
Sugar Phosphate ◽  
Kinetic Isotope

Rate constants are reported for the reaction of muonium atoms in water with some 36 organic compounds, many of interest in biology. These kM values range from < l05 to 7 × 1010 M−1 s−1, according to the type of reaction involved, with the sugar–phosphate backbones of nucleic acids being at the low end and their bases at the high end. They are compared with corresponding published H-atom data (kH), where possible, and show kinetic-isotope-effects ranging over five orders of magnitude. Since all kH data were obtained at pH = 1, while kM values refer to pH ~ 7 of the natural state, the pH-dependence of kM was examined in representative cases. The changes found result from protonation of the solute rather than a changed reactivity of Mu on being converted to MuH+. On localizing the solutes in the hydrophobic phase of dilute micelles, the reactivity of Mu was again measured (kM(mic)). The resulting "enhancement" factor was considered in terms of: the reaction mechanism, its dependence on microenvironment (solvation), and the concentrating effect of mutual confinement to small sections of a biphasal system. Key words: kinetic isotope effects, muonium, biochemicals, micelles.

Kinetic and solvent isotope effects in oxidation of halogen derivatives of tyramine catalyzed by monoamine oxidase A

2019 ◽  
Vol 167 (1) ◽  
pp. 49-54
Author(s):  
Małgorzata Pająk
Keyword(s):  
Monoamine Oxidase ◽  
Isotope Effect ◽  
Isotope Effects ◽  
Monoamine Oxidase A ◽  
Oxidative Deamination ◽  
Solvent Isotope Effect ◽  
Kinetic Isotope ◽  
Solvent Isotope ◽  
Derivatives Of ◽  
Solvent Isotope Effects

Abstract The isotope effects approach was used to elucidate the mechanism of oxidative deamination of 3′-halotyramines, catalyzed by monoamine oxidase A (EC 1.4.3.4). The numerical values of kinetic isotope effect (KIE) and solvent isotope effect (SIE) were established using a non-competitive spectrophotometric technique. Based upon KIE and SIE values, some of the mechanistic details of investigated reaction were discussed.

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