Alkaline phosphatase catalyzes the hydrolysis and transphosphorylation of phosphomonoesters (1). A kinetic reaction scheme of AP is presented in Figure 2.
Figure 2: Kinetic reaction scheme of alkaline phosphatase (11). Under the hydrolysis reaction, free phosphate and an alcohol molecule are released from the active site. The rate-determining step of this reaction is pH dependent. Transphosphorylation has similar initiate steps as hydrolysis. However, phosphate cannot exit the active site, and it will transfer to an acceptor. This will form a new phosphomonoester molecule.
Figure 3: Two metal ions catalysis mechanism of E. coli alkaline phosphatase (9). Zn(II) ions and essential amino acids are shown while Mg(II) ion is not displayed. Both Zn(II) ions seem to serve two primary functions. Zn1 facilitates the leaving of an alcohol group in the first step of the reaction while Zn2 activates Ser102 residue to induce a nucleophilic attack. Despite this difference, both ions stabilize the negative charges of phosphate in the active site.
As proposed by Kim and Wyckoff, Zn(II) ions have direct impacts in alkaline phosphatase catalytic reactions (9). The first step of reaction occurs when AP …show more content…
One question may arise during this step would be how can serine be deprotonated. AP functions at maximal efficiency in pH 8 buffer solutions, and the pKa value of the hydroxyl group of serine is undefined. Thus, it is unlikely that serine loses a proton in the solution. How serine loses its proton is still not fully understood. Despite the ambiguity in deprotonation of a serine residue, Zn(II) ion at M2 position then stimulates Ser102 to attack the phosphorus center of the substrate to initiate the leaving of an alcohol group and to form a phosphoseryl intermediate. This intermediate resembles E-Pi, an enzyme-phosphate complex, in Figure 2 and
Figure 2: Kinetic reaction scheme of alkaline phosphatase (11). Under the hydrolysis reaction, free phosphate and an alcohol molecule are released from the active site. The rate-determining step of this reaction is pH dependent. Transphosphorylation has similar initiate steps as hydrolysis. However, phosphate cannot exit the active site, and it will transfer to an acceptor. This will form a new phosphomonoester molecule.
Figure 3: Two metal ions catalysis mechanism of E. coli alkaline phosphatase (9). Zn(II) ions and essential amino acids are shown while Mg(II) ion is not displayed. Both Zn(II) ions seem to serve two primary functions. Zn1 facilitates the leaving of an alcohol group in the first step of the reaction while Zn2 activates Ser102 residue to induce a nucleophilic attack. Despite this difference, both ions stabilize the negative charges of phosphate in the active site.
As proposed by Kim and Wyckoff, Zn(II) ions have direct impacts in alkaline phosphatase catalytic reactions (9). The first step of reaction occurs when AP …show more content…
One question may arise during this step would be how can serine be deprotonated. AP functions at maximal efficiency in pH 8 buffer solutions, and the pKa value of the hydroxyl group of serine is undefined. Thus, it is unlikely that serine loses a proton in the solution. How serine loses its proton is still not fully understood. Despite the ambiguity in deprotonation of a serine residue, Zn(II) ion at M2 position then stimulates Ser102 to attack the phosphorus center of the substrate to initiate the leaving of an alcohol group and to form a phosphoseryl intermediate. This intermediate resembles E-Pi, an enzyme-phosphate complex, in Figure 2 and