The narrow substrate specificity of human tyrosine aminotransferase--the enzyme deficient in tyrosinemia type II.

摘要: Human tyrosine aminotransferase (hTATase) is the pyridoxal phosphate-dependent enzyme that catalyzes reversible transamination of to p-hydrophenylpyruvate, an important step in metabolism. hTATase deficiency implicated rare metabolic disorder, tyrosinemia type II. This a member poorly characterized Iγ subfamily family I aminotransferases. The full length and truncated forms recombinant were expressed Escherichia coli, purified homogeneity. pH-dependent titration wild-type reveals spectrum characteristic aminotransferases with aldimine pKa 7.22. I249A mutant exhibits unusual similar (6.85). has very narrow substrate specificity highest enzymatic activity for Tyr/α-ketoglutarate pair, which gives steady state kcat value 83 s−1. In contrast there no detectable aspartate or other cosubstrates. present findings show only known discriminates significantly between Tyr Phe: kcat/Km about four orders magnitude greater than Phe. A comparison specificities representative Iα described along physiological significance discrimination Phe by as applied understanding molecular basis phenylketonuria.