Steventon Glyn B, Mitchell Stephen C, Pérez Belen, Desviat Lourdes R, Ugarte Magdalena
King's College London, Pharmaceutical Science Division, Franklin Wilkins Building, 150 Stamford Street, London SE1 9NH, UK.
Mol Genet Metab. 2009 Jan;96(1):27-31. doi: 10.1016/j.ymgme.2008.10.011. Epub 2008 Nov 25.
The involvement of the enzyme, phenylalanine hydroxylase (PAH), in the S-oxidation of S-carboxymethyl-L-cysteine (SCMC) is now firmly established in man and rat. However, the underlying role of the molecular genetics of PAH in dictating and influencing the S-oxidation polymorphism of SCMC metabolism is as yet unknown. In this work we report that the S-oxidation of SCMC was dramatically reduced in the tetrahydrobiopterin (BH(4)) responsive mutant PAH proteins (I65T, R68S, R261Q, V388M and Y414C) with these enzymes possessing between 1.2% and 2.0% of the wild type PAH activity when SCMC was used as substrate. These same mutant proteins express between 23% and 76% of the wild type PAH activity when phenylalanine was used as the substrate. The PAH mutant proteins (R158Q, I174T and R408W) that result in the classical phenylketonuria (PKU) phenotype expressing 0.2-1.8% of the wild type PAH activity when using phenylalanine as substrate were found to have <0.1% of the wild type PAH activity when SCMC was used as the substrate. Mutations that result in PAH proteins retaining some residual PAH activity with phenylalanine as substrate have <2.0% residual activity when SCMC was used as a substrate. This investigation has led to the hypothesis that the S-oxidation polymorphism in man is a consequence of an individual carrying one mutant PAH allele which has resulted in the loss of the ability of the residual PAH protein to undertake the S-oxidation of SCMC in vivo.
现已确定，在人和大鼠体内，酶苯丙氨酸羟化酶（PAH）参与了S-羧甲基-L-半胱氨酸（SCMC）的S-氧化过程。然而，PAH分子遗传学在决定和影响SCMC代谢的S-氧化多态性方面的潜在作用尚不清楚。在本研究中，我们报告称，当以SCMC为底物时，四氢生物蝶呤（BH(4)）反应性突变型PAH蛋白（I65T、R68S、R261Q、V388M和Y414C）的S-氧化显著降低，这些酶的活性仅为野生型PAH活性的1.2%至2.0%。当以苯丙氨酸为底物时，这些相同的突变蛋白表达的野生型PAH活性为23%至76%。导致经典苯丙酮尿症（PKU）表型的PAH突变蛋白（R158Q、I174T和R408W），以苯丙氨酸为底物时表达的野生型PAH活性为0.2 - 1.8%，而以SCMC为底物时，其活性低于野生型PAH活性的0.1%。导致PAH蛋白以苯丙氨酸为底物时仍保留一些残余PAH活性的突变，以SCMC为底物时其残余活性<2.0%。这项研究提出了一个假设，即人类中的S-氧化多态性是个体携带一个突变PAH等位基因的结果，该等位基因导致残余PAH蛋白在体内丧失了对SCMC进行S-氧化的能力。
