Quantum-Mechanical Study on the Catalytic Mechanism of Alkaline Phosphatases

Elevated serum alkaline phosphatase correlates with postoperative cognitive dysfunction: A retrospective cohort study based on STROBE statement

Little is known about the association between serum alkaline phosphatase (ALP) levels and postoperative cognitive dysfunction (POCD) after general anesthesia. Thus, we investigated the association of serum ALP levels with POCD in patients who underwent surgery with general anesthesia in a retrospective cohort study. We retrospectively collected data from patients who underwent surgery with general anesthesia between May 2016 and June 2020. Serum ALP activity was detected using a p-nitrophenyl phosphate assay. Pre-and postoperative cognitive function were evaluated using the Chinese version of the Mini-Mental State Examination. Univariate and multivariate logistic regression were used to explore the effect of ALP on cognitive function. The incidence of POCD was 13.5%. Compared with the control group, the POCD group had higher ALP levels. The neuropsychological test results suggested that the scores of most items were lower in the POCD group than in the non-POCD group. Univariate logistic regression indicated that increased ALP levels were significantly associated with cognitive dysfunction (odds ratio = 1.15, 95% confidence interval: 1.13-1.18, P = .000). Multivariate regression showed that elevated ALP was still associated with POCD after adjusting for confounding factors (odds ratio = 1.16, 95% confidence interval: 1.13-1.18, P = .000). The spline regression model indicated the dose-response associations between ALP level and POCD risk (P for nonlinear trend < .001). Our study indicated that elevated serum ALP was an independent predictive factor of POCD at the 3-month follow-up. The occurrence of POCD could be associated with inflammatory status.

Promiscuous Catalytic Activity of a Binuclear Metallohydrolase: Peptide and Phosphoester Hydrolyses

In this study, chemical promiscuity of a binuclear metallohydrolase Streptomyces griseus aminopeptidase (SgAP) has been investigated using DFT calculations. SgAP catalyzes two diverse reactions, peptide and phosphoester hydrolyses, using its binuclear (Zn-Zn) core. On the basis of the experimental information, mechanisms of these reactions have been investigated utilizing leucine p-nitro aniline (Leu-pNA) and bis(4-nitrophenyl) phosphate (BNPP) as the substrates. The computed barriers of 16.5 and 16.8 kcal/mol for the most plausible mechanisms proposed by the DFT calculations are in good agreement with the measured values of 13.9 and 18.3 kcal/mol for the Leu-pNA and BNPP hydrolyses, respectively. The former was found to occur through the transfer of two protons, while the latter with only one proton transfer. They are in line with the experimental observations. The cleavage of the peptide bond was the rate-determining process for the Leu-pNA hydrolysis. However, the creation of the nucleophile and its attack on the electrophile phosphorus atom was the rate-determining step for the BNPP hydrolysis. These calculations showed that the chemical nature of the substrate and its binding mode influence the nucleophilicity of the metal bound hydroxyl nucleophile. Additionally, the nucleophilicity was found to be critical for the Leu-pNA hydrolysis, whereas double Lewis acid activation was needed for the BNPP hydrolysis. That could be one of the reasons why peptide hydrolysis can be catalyzed by both mononuclear and binuclear metal cofactors containing hydrolases, while phosphoester hydrolysis is almost exclusively by binuclear metallohydrolases. These results will be helpful in the development of versatile catalysts for chemically distinct hydrolytic reactions.

Alkaline Phosphatases: in Silico Study on the Catalytic Effect of Conserved Active Site Residues Using Human Placental Alkaline Phosphatase (PLAP) As a Model Protein

The metalloenzymes from the alkaline phosphatase (AP) superfamily catalyze the hydrolysis and transphosphorylation of phosphate monoesters. The role of several amino acids highly conserved in the active site of this family of enzymes was examined, using human placental AP (PLAP) as a model protein. By employing an active-site model based on the X-ray crystal structure of PLAP, mutations of several key residues were modeled by quantum mechanical methods in order to determine their impact on the catalytic activity. Kinetic and thermodynamic estimations were achieved for each reaction step of the catalytic mechanism by characterization of the intermediates and transition states on the reaction pathway, and the effects of mutations on the activation barriers were analyzed. A good accordance was observed between the present computational results and experimental measurements reported in the literature.