title: Kinetic properties of bovine pineal tryptophan-5-monooxygenase activated by an endogenous activating substance.
abstract: 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 Km's for substrates, L-tryptophan and oxygen, and coenzyme, reduced biopterin or DMPH4; but that it increases the Vmax 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 Km's for reduced biopterin and DMPH4 were 77.2 microM and 294 microM, respectively. The apparent Km's for L-tryptophan and oxygen with reduced biopterin were 15.0 microM and 4.7%, respectively; with DMPH4, they were 11.0 microM and 8.5%, respectively. Significant inhibition of both L-tryptophan and oxygen was observed with reduced biopterin, but not with DMPH4 (at the tested concentrations of up to 0.5 mM and 20%, respectively).
mesh_terms: D000818:Animals; D001708:Biopterins / Q000494:pharmacology; D002417:Cattle; D004789:Enzyme Activation; D007700:Kinetics; D010084:Oxidation-Reduction; D010870:Pineal Gland / Q000201:enzymology*; D014357:Trypsin / Q000378:metabolism; D014365:Tryptophan Hydroxylase / Q000378:metabolism*
chemical_list: D001708:Biopterins; D014365:Tryptophan Hydroxylase; D014357:Trypsin