[Kinetic model and mechanism of regulation of a multienzyme system of thromboxane synthesis].

A kinetic model has been suggested for the thromboxane synthesis polyenzyme system, taking into account the inactivation of a limiting enzyme, prostaglandin H-synthetase, in the course of the reaction. The model also includes the effect of phospholipase, adenylate cyclase, as well as the "outflows" of the components from the system, and basic regulatory effects in the system. A mathematical description of the model is given, and numerical solutions of the system of equations obtained for a wide variety of parameters. An analysis of the kinetic responses of the polyenzyme system shows that: 1) the system is highly conserved with respect to thromboxane concentration changes; 2) two cardinally different modes of the system are registered; they correspond to two insignificantly differing thromboxane steady-state levels; 3) transition of the system from one mode to the other is controlled by the phospholipase activity level which is sensitive to a change in the concentration of the regulator (cyclo-AMP or Ca ions) in the system. It is presumed that the two thromboxane steady-state levels are of physiological significance.