Enzymatic reaction kinetics of L-Arginine

Studies on the enzyme-catalyzed reaction kinetics of L-Arginine involve multiple enzymes and their catalytic reaction processes. The relevant content is as follows:

I. Kinetics of Arginase-Catalyzed Reactions

Michaelis Constant and Maximum Reaction Rate

Under the conditions of 40 mmol/L sodium barbital-HCl buffer solution (pH = 9.4) and 37°C, in the reaction where arginase catalyzes the hydrolysis of L-arginine into L-ornithine and urea, the Michaelis constant (Km) of arginine is 5.14 mmol/L, and the maximum reaction rate (Vm) is 1.13×10⁻² mmol/(L·s).

Substrate Inhibition and Competitive Inhibition

L-ornithine, a product of the arginase-catalyzed reaction, exerts an inhibitory effect on the reaction, with a product inhibition constant (KP) of 1.18 mmol/L. In addition, exogenous L-lysine can also cause competitive inhibition of arginase, with an inhibition constant (KI) of 5.6 mmol/L. Meanwhile, calf liver arginase is also competitively inhibited by L-ornithine, with an inhibition constant (KI) of 480 mM.

Optimal Reaction Conditions

For arginase purified from buffalo liver, the optimal pH and temperature are 9.5 and 40°C, respectively. Adding dihydropyrimidine derivatives and metal ions (such as Mn²⁺ and Mg²⁺) to the reaction medium can activate arginase, reducing its Km value and increasing its Vmax value—indicating that these substances can enhance the activity of arginase.

II. Kinetics of Arginine Kinase-Catalyzed Reactions

Arginine kinase can catalyze the reversible transfer of the terminal phosphate group of ATP to L-arginine. At pH 7.25 and 12°C, the equilibrium constant under the catalytic enzyme concentration (Keq_eq = [MgADP][P-arginine]/[MgATP][L-arginine]) is 0.10±0.02, and the equilibrium constant under the stoichiometric enzyme concentration (K'eq = [E-MgADP][E-P-arginine]/[E-MgATP][E-arginine]) is 1.56±0.5. An increase in enzyme concentration is more conducive to the formation of P-arginine. NMR line shape analysis shows that in the presence of excess enzyme, the rate of phosphate group transfer on the enzyme surface in the forward reaction (starting from E-MgATP) is 192±15 s⁻¹, and the rate of the reverse reaction is 154±15 s⁻¹.

III. Kinetics of Arginine Deiminase-Catalyzed Reactions

Arginine deiminase (EC 3.5.3.6) can catalyze the hydrolysis of L-arginine into citrulline and ammonium ions. At 25°C, a rapid quenching study on the single-turnover reaction using recombinant Pseudomonas aeruginosa arginine deiminase showed that the apparent rate constant (k) for citrulline formation is 3.6±0.1 s⁻¹, the apparent rate constant (k) for arginine decay is 4.2±0.1 s⁻¹, the formation rate constant (k) of ¹⁴C-labeled enzyme is 13 s⁻¹, and the decay rate constant (k) is 6.5 s⁻¹. These results indicate the presence of a kinetically effective intermediate during the reaction.