Screening and development of enzymes for determination and transformation of amino acids

Fe3O4@SiO2@NiAl-LDH microspheres implication in separation, kinetic and structural properties of phenylalanine dehydrogenase

Fe3O4@SiO2@NiAl-LDH three-components microsphere contains a Fe3O4@SiO2 magnetic core and a layered double hydroxide with nickel cation provide the binding ability to (His)-tagged-protein and exhibits high performance in protein separation and purification. The morphology and chemistry of the synthesized Fe3O4@SiO2@NiAl-LDH microspheres were characterized by energy-dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR), vibrating sample magnetometer (VSM), Dynamic light scattering (DLS). Purified enzyme was assesed with SDS-PAGE (sodium dodecyl sulfate-polyacrylamide gel electrophoresis and intrinsic fluorescence spectroscopy. In this study, the separation of phenylalanine dehydrogenase (PheDH) by Fe3O4@SiO2@NiAl -LDH was performed and the effect of microsphere was investigated on the kinetic and structural properties of PheDH. After purification, kinetic parameters such as Km, Vmax, Kcat, kcat/Km, optimum temperature, thermal stability, and and activation energy were evaluated and compared according to the mentioned methods. The interaction between the enzyme and the microsphere displayed a high performance in protein binding capacity. The results also revealed that the kinetic parameters of the enzyme changed in a dose-dependent manner in the presence of a microsphere. Moreover, the results of intrinsic fluorescence and Circular Dichroism (CD) confirmed the structural changes of the protein in the interaction with the microsphere.

Comparison of Tandem Mass Spectrometry and the Fluorometric Method-Parallel Phenylalanine Measurement on a Large Fresh Sample Series and Implications for Newborn Screening for Phenylketonuria

Phenylketonuria (PKU) was the first disease to be identified by the newborn screening (NBS) program. Currently, there are various methods for determining phenylalanine (Phe) values, with tandem mass spectrometry (MS/MS) being the most widely used method worldwide. We aimed to compare the MS/MS method with the fluorometric method (FM) for measuring Phe in the dried blood spot (DBS) and the efficacy of both methods in the NBS program. The FM was performed using a neonatal phenylalanine kit and a VICTOR2^TM D fluorometer. The MS/MS method was performed using a NeoBase^TM 2 kit and a Waters Xevo TQD mass spectrometer. The Phe values measured with the MS/MS method were compared to those determined by the FM. The cut-off value for the NBS program was set at 120 µmol/L for FM and 85 µmol/L for MS/MS. We analyzed 54,934 DBS. The measured Phe values varied from 12 to 664 µmol/L, with a median of 46 µmol/L for the MS/MS method and from 10 to 710 µmol/L, with a median of 70 µmol/L for the FM. The Bland-Altman analysis indicated a bias of -38.9% (-23.61 µmol/L) with an SD of 21.3% (13.89 µmol/L) when comparing the MS/MS method to the FM. The Phe value exceeded the cut-off in 187 samples measured with FM and 112 samples measured with MS/MS. The FM had 181 false positives, while the MS/MS method had 106 false positives. Our study showed that the MS/MS method gives lower results compared to the FM. Despite that, none of the true positives would be missed, and the number of false-positive results would be significantly lower compared to the FM.

Novel Enzymatic Method for Imine Synthesis via the Oxidation of Primary Amines Using D-Amino Acid Oxidase from Porcine Kidney

During studies on the oxidative cyanation reaction catalyzed by a variant of D-amino acid oxidase from porcine kidney (pkDAO) (Y228L/R283G), an unexpected formation of 1-phenyl-N-(1-phenylethylidene)ethanamine (PPEA) was detected. The optimal reaction conditions for the synthesis of PPEA and the reaction mechanism were investigated using the pkDAO variant. The highest PPEA synthesis was obtained in the reaction with 150 mM (R)-MBA at pH 9.0 and at 20 °C. Since PPEA synthesis proceeded by trapping the intermediate 1-phenylethanimine (1-PEI) by 15N-labeled n-hexylamine, which is not a substrate for the pKDAO variant, it was deduced that PPEA would be synthesized by a nucleophilic substitution of 1-PEI by another molecule of (R)-MBA. PPEA was further identified by its conversion to bis(1-phenylethyl)amine (BPEA) through reduction with NaBH4. Thus, a new enzymatic method of imine synthesis by oxidation of primary amine by the variant pkDAO was achieved for the first time.

Identification of l-histidine oxidase activity in Achromobacter sp. TPU 5009 for l-histidine determination

An enzyme showing l-histidine oxidase (HisO) activity by the formation of hydrogen peroxide was newly purified from Achromobacter sp. TPU 5009. This enzyme was found to be a heterodimer of two proteins (molecular mass, 53.8 and 58.3 kDa), the partial determination of which indicated they are homologs of l-histidine ammonia-lyase (AchHAL) and urocanate hydratase (AchURO). The enzyme was stable in a pH range of 5.0-11.0, with >90% of the original activity maintained below 60°C at pH 7.0. To characterize AchHAL and AchURO, each of their genes was cloned and expressed in a heterologous expression system. Heterologous AchHAL catalyzed the elimination of the α-amino group of l-histidine to urocanate and ammonia, while heterologous AchURO catalyzed the hydration of urocanate to imidazolone propionate. Since imidazolone propionate is highly unstable in the presence of oxygen at neutral pH, it was immediately decomposed and hydrogen peroxide was non-enzymatically produced. Our results indicate that this natural enzyme showing apparent HisO activity is composed of AchHAL and AchURO, which formed hydrogen peroxide after the spontaneous decomposition of imidazolone propionate.

Development of a rapid and simple glycine analysis method using a stable glycine oxidase mutant

Glycine analysis is important in research fields such as physiology and healthcare because the concentration of glycine in human plasma has been reported to change with various disorders. Glycine oxidase from Bacillus subtilis (GlyOX) is useful for quantitative analysis of glycine. However, GlyOX is not sufficiently stable for use in physiology-based research or clinical settings. In this report, site-directed mutagenesis was used to engineer a GlyOX mutant suitable for glycine analysis. The GlyOX triple-mutant (T42 A/C245 S/L301V) retained most of its enzymatic activity during storage for over a year at 4 °C. A colorimetric enzyme analysis protocol was established using the GlyOX triple-mutant to determine glycine concentrations in human plasma. The analysis showed high accuracy (-5.4 to 3.5% relative errors when compared with the results from an amino acid analyzer, and 96.0-98.7% recoveries) and high precision (<4% between-run variation). Sample pretreatments of deproteinization and derivatization were not required. Therefore, this novel enzymatic analysis offers an effective and useful method for determining glycine concentrations in physiology related research and the healthcare field.