Scattering kinetics in a complex tryptophan hydroxylase preparation from rat brainstem raphe nuclei: statistical evidence that the lithium-induced sigmoid velocity function reflects two states of available catalytic potential.

Multiple measures on statistical patterns from a kinetic scattering paradigm for the activities of rat brainstem medial and dorsal raphé nuclear tryptophan hydroxylase preparations are consistent with the previous hypothesis (J. Neural Transmission 45: 1-15, 1979) that the lithium ion induces a state of kinetic bistability in the system. In this context, the lithium-induced sigmoid tetrahydrobiopterin-reaction velocity function is interpreted as a jump between two stable states of differing catalytic potential with a less kinetically accessible domain between them. These dynamics are qualitatively portrayed in three dimensions by Thom's classical cusp catastrophe.