A Biochemical Method for Tyrosine Determination in Phenylketonuria Using a Colorimetric Enzymatic Approach

Abstract

Phenylketonuria is a serious genetic disease caused by a deficiency of phenylalanine metabolism, an essential amino acid found in daily nutrition. This disorder is caused by the lack of a specific enzyme called phenylalanine hydroxylase which mediates the conversion of phenylalanine to tyrosine). Thus, after ingestion of phenyl alanine-rich proteins, the amino acid concentration increases considerably in the blood due to proteolysis. Genetic deffects of enzymes responsible for phenylalanine metabolic conversion were intensively studied. Among them the defect of gene encoding phenylalanine hydroxylase has a higher notoriety. This genetic defect is translated in an inactive enzyme constructs that impair the aminoacid hydroxylation. This physiological stage is also called hyperphenylalaninemia where slightly high levels of phenylalanine are noticed in the blood or urine. Consequently, the amino acid is converted to phenylpyruvic acid by transamination, the later displaying a particularly toxic effect against brain tissues. The aim of this study was to quantify tyrosine in the blood of patients suffering of phenylketonuria by an alternative enzymatic method. The tyrosinase used in this assay was extracted from commercial mushrooms (Agaricus bisporus) following the Haghbeen protocol with some modifications. Two chromatographic steps (molecular exclusion chromatography and ionic exchange chromatography) were used during the enzyme purification process. High purity samples were concentrated using ultrafiltration. The tyrosinase was screened by a classical enzymatic microplate assay having DOPA as a substrate. Finally the pure enzyme was used in order to quantify tyrosine from different standard solutions. The level of tyrosine from deproteinized serum samples was determined using a similar enzymatic strategy.

Electrochemical sensor based on molecularly imprinted copolymer for selective and simultaneous determination of Ascorbic acid and Tyrosine

“…Its presence is very essential as responsible for regulating protein synthesis and functions as a precursor for the neurotransmitters containing epinephrine, norepinephrine, and dopamine [3]. An abnormality in the level of Tyr leads to depression and various diseases including albinism, alkaptonuria, Parkinson's, liver disease, tyrosinemia, mental illness, and lung disease [4][5][6]. Ascorbic acid (AA) or ascorbate, also called as vitamin C, is a signi cant watersoluble vitamin essential in human nutrition which derived from fruits and green vegetables [7,8].…”

Novel Design of Neuropeptide-Based Drugs with β-Sheet Breaking Potential in Amyloid-Beta Cascade: Molecular and Structural Deciphers

“…Due to their low intrinsic toxicity, peptides are particularly appealing. The use of highly effective and precise peptide drugs would considerably help neurological conditions such as neurodegeneration, pain, psychiatric disorders, stroke and brain tumors [ 21 , 22 , 23 ]. As a result of advancements in biotechnology, a wide range of peptide drugs are currently produced on a commercial basis.…”

Zinc Binding to NAP-Type Neuroprotective Peptides: Nuclear Magnetic Resonance Studies and Molecular Modeling

“…For instance, the neuroprotective 1 NAPVSIPQ 8 peptide (NAP) contains two prolines, which confer β conformation. The potential activity of this peptide consist of the inhibition of Aβ and Aβ (25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35) fibrillogenesis, protection against Aβ-induced neurotoxicity, and prevention of AD-associated microtubule disruption [17].…”

“…Hence, the Tyr choice was made for this reason as well, since it allowed us to follow the influence on Zn complex formation. In addition, Tyr can be easily oxidized to dihydroxyphenylalanine (DOPA), a precursor used in the treatment of Parkinson's disease [31]. Thus, following the oxidation process, a new hydroxyl group liable to intervene in metal complexation is introduced.…”