TRH influences the pterin cofactor- and time-dependent instabilities of rat raphe tryptophan hydroxylase activity...

Systematic effects on the dynamics of rat raphé tryptophan hydroxylase were observed in the presence of thyrotropin-releasing hormone under the far-from-equilibrium conditions of a kinetic scattering paradigm. The peptide reduced the amplitude of velocity fluctuations across fine-grained increases in cofactor or time and induced rare, high-amplitude irregularities suggesting phase transitions at relatively long wavelengths. Respectively, these two effects of the neuropeptide resemble the statistical changes observed in the same enzyme system in the presence of the lithium ion and the tricyclic antidepressant chlorimipramine under comparable assay conditions. Neither the subtleties of control dynamics nor their responses to the peptide were demonstrable under the saturating conditions of Michaelis-Menten or allosteric kinetics. These findings have possible implications for neurotransmitter regulation in view of the most current information about dynamical interactions among proteins, peptides, and ion ligands in aqueous environment.