中島 昭

We first identified GTP cyclohydrolase I activity (EC 3.5.4.16) 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 dope, the substrate of aromatic L-amino acid decarboxylase, could not be detected in this protozoa. Furthermore, neither dopamine B-hydroxylase activity nor phenylethanolamine N-methyltransferase activity could be identified by the HPLC methods. (C) 1998 Elsevier Science Inc. All rights reserved.

We found that high molecular polyanions (PAs) such as dextran sulfate and heparin burst some damaged or dead lymphocytes in lymphocyte suspension isolated from living bodies, and clarified morphologically the mechanism involved in this. PAs passed through damaged cell membranes and reached the chromatin in the nucleus. Electron micrographs suggested that they then extracted histones from the chromatin and formed complexes with them, and that freed DNA formed a gel binding with the complexes in the nucleus, and the nucleus became swollen and burst due to the gel swelling pressure. To support this conjecture, the nuclei of lymphocytes were stained with propidium iodide and exposed to light to stabilize them, The stabilized nuclei were not swollen after the addition of PAs and the lymphocytes did not burst. The lymphocyte bursting effect of PAs was attributed to their negative charges which could not destroy intact cells. At this point, PAs are different from sodium dodecyl sulfate which destroys intact cells completely. (C) 1997 Academic Press.