Enzymes related to catecholamine biosynthesis in Tetrahymena pyriformis. Presence of GTP cyclohydrolase I

Takahide Nomura, Masahiro Tazawa, Masatsugu Ohtsuki, Chiho Sumi-Ichinose, Yasumichi Hagino, Akira Ota, Akira Nakashima, Keiji Mori, Takashi Sugimoto, Osamu Ueno, Yoshinori Nozawa, Hiroshi Ichinose, Toshiharu Nagatsu

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10 Citations (Scopus)


We first identified GTP cyclohydrolase I activity (EC in the ciliated protozoa, Tetrahymena pyriformis. The V(max) value of the enzyme in the cellular extract of T. pyriformis was 255 pmol mg-1 protein h-1. Michaelis-Menten kinetics indicated a positive cooperative binding of GTP to the enzyme. The GTP concentration producing half-maximal velocity was 0.8 mM. By high-performance liquid chromatography (HPLC) with fluorescence detection, a major peak corresponding to d-monapterin (2-amino-4-hydroxy-6-[(1'R,2'R)-1',2',3'-trihydroxypropyl]pteridine, d-threo-neopterin) and minor peaks of d-erythro-neopterin and l-erythro-biopterin were found to be present in the cellular extract of Tetrahymena. Thus, it is strongly suggested that Tetrahymena converts GTP into unconjugated pteridine derivatives. In this study, dopamine was detected as the major catecholamine, while neither epinephrine nor norepinephrine was identified. Indeed, this protozoa was shown to possess the activity of a dopamine synthesizing enzyme, aromatic l-amino acid decarboxylase. On the other hand, activities of tyrosine hydroxylase or tyrosinase which converts tyrosine into dopa, the substrate of aromatic l-amino acid decarboxylase, could not be detected in this protozoa. Furthermore, neither dopamine β-hydroxylase activity nor phenylethanolamine N-methyltransferase activity could be identified by the HPLC methods. Copyright (C) 1998 Elsevier Science Inc.

Original languageEnglish
Pages (from-to)753-760
Number of pages8
JournalComparative Biochemistry and Physiology - B Biochemistry and Molecular Biology
Issue number4
Publication statusPublished - 1998

All Science Journal Classification (ASJC) codes

  • Biochemistry
  • Physiology
  • Molecular Biology


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