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Kinetic Properties of Bovine Pineal Tryptophan‐5‐Monooxygenase Activated by an Endogenous Activating Substance
Author(s) -
Hori Shinichiro,
Ohtani Sachiko
Publication year - 1981
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1981.tb01627.x
Subject(s) - biopterin , tryptophan , chemistry , monooxygenase , biochemistry , trypsin , endogeny , bovine serum albumin , enzyme , cofactor , amino acid , tetrahydrobiopterin , cytochrome p450
We previously reported that an endogenous activating substance different from bovine serum albumin, phospholipids and heparin, exists in the extract from bovine pineal glands and that this substance interacts with tryptophan‐5‐monooxygenase under reducing conditions with sulfhydryl reagents, to stimulate monooxygenase activity. The present paper reports that the activating substance is of peptide nature; that it is sensitive to trypsin‐digestion; and that it does not change the apparent K m 's for substrates, L‐tryptophan and oxygen, and coenzyme, reduced biopterin or DMPH 4 : but that it increases the V max 1.5‐ to 2.3‐fold. These results suggest that an activating protein, present in some particles of the cell structure, activates tryptophan‐5‐monooxygenase under the regulation of a sulfhydryl compound. The apparent K m 's for reduced biopterin and DMPH 4 were 77.2μM and 294 μM, respectively. The apparent K m 's for L‐tryptophan and oxygen with reduced biopterin were 15.0 μM and 4.7%, respectively: with DMPH 4 , they were 11.0 μM and 8.5%, respectively. Significant inhibition of both L‐tryptophan and oxygen was observed with reduced biopterin, but not with DMPH 4 (at the tested concentrations of up to 0.5 MM and 20%, respectively).