pocket: His 23,48 and 50. Residues Cys42, Glu133, and His89 are in close proximity to the binding pocket but are not binding it. These are thought to serve as proton donors and acceptors during catalysis. The cofactor bound can be either Mg2+ or Ni2+ (Protein Database). As previously mentioned it is involved in the biosynthesis of BH4 and catalyzes the transformation of 7,8-dihydroneopterin triphosphate into 6-pyruvoyl tetrahydropterin synthase. The kinetic values for this enzyme are KM = 8.1 μM and Vmax = 120 nmol/min/mg. The structure of PTPS is unique and is different than other examples of antiparallel 𝛃-barrels. It is described as being formed by "a three-fold symmetrical arrangement of subunits". A similar 𝛃-barrel formation has been discovered in CKS2, the difference between PTPS and CKS2 is that the formation of the latter is metal induced and reversible. The PTPS trimer is similar to a porin and is hypothesized to serve as a tunnel for dihydroneopterin triphosphate. Diagnosis PTPS deficiency can usually be detected by the same screening test used for PKU, because both disorders result in elevated levels of Phenylalanine. This test is known as the Guthrie test and is done on babies a few days after birth. Another diagnostic method is to measure Pteridine levels in urine and to measure neurotransmitters 5-hydroxyindolacetic acid (5-HIAA) and homovanillic acid (HVA). Epidemiology Taiwanese Chinese are more likely to get PTPS deficiency as the prevalence in Taiwanese Chinese is about 1/132,000 compared to white individuals at about 1/1,000,000. The image below illustrates frequency of different BH4 deficiency defects. This is suggested to be due to the Founder effect. The smaller pie charts on the side illustrate the incidence of DHPR and PTPS deficiency around the world. As can be seen PTPS deficiency occurs most commonly in Asian countries and this makes sense because of the incidence of this disease in Taiwanese Chinese being significantly higher than any other population. History PTPS deficiency is not necessarily its own disease. It shares history with PKU and hyperphenylalaninemia (HPA) . Asbjørn Følling, a physician studying metabolic diseases, identified an excess of phenylpyruvate as the cause of a strange, musty odor from the urine of two Norwegian children. Further research by Penrose in 1935 lead to the coining of the term, “phenylketonuria”. The foundations for dietary restrictions were laid down by George Jervis and Host Bickel which is still one of the best ways to