Abstract
The kinetic model of Prostaglandin H Synthase-1 (PGHS-1) was developed to investigate its complex network kinetics and non-steroidal anti-inflammatory drugs (NSAIDs) efficacy in different in vitro and in vivo conditions. To correctly describe the complex mechanism of PGHS-1 catalysis, we developed a microscopic approach to modelling of intricate network dynamics of 35 intraenzyme reactions among 24 intermediate states of the enzyme. The developed model quantitatively describes interconnection between cyclooxygenase and peroxidase enzyme activities; substrate (arachidonic acid, AA) and reducing cosubstrate competitive consumption; enzyme self-inactivation; autocatalytic role of AA; enzyme activation threshold; and synthesis of intermediate prostaglandin G2 (PGG2) and final prostaglandin H2 (PGH2) products under wide experimental conditions. In the paper, we provide a detailed description of the enzyme catalytic cycle, model calibration based on a series of in vitro kinetic data, and model validation using experimental data on the regulatory properties of PGHS-1. The validated model of PGHS-1 with a unified set of kinetic parameters is applicable for in silico screening and prediction of the inhibition effects of NSAIDs and their combination on the balance of pro-thrombotic (thromboxane) and anti-thrombotic (prostacyclin) prostaglandin biosynthesis in platelets and endothelial cells expressing PGHS-1.
Highlights
Prostaglandin H synthase-1 (PGHS-1), known as Cyclooxygenase-1 (COX-1), catalyses the first stage in the conversion of arachidonic acid (AA) into prostaglandin H2 (PGH2), being a precursor of physiologically active prostanoids [1]
The derivation of the model of PGHS-1 catalysis represents a special task, as both POX and COX activities are known to be located in different enzyme domains within the same protein complex, and these activities can proceed independently of each other [18]
Another important feature of PGHS-1 catalysis is that it involves intramolecular electron transfer and formation of multiple redox and binding states of the catalytic domain
Summary
Prostaglandin H synthase-1 (PGHS-1), known as Cyclooxygenase-1 (COX-1), catalyses the first stage in the conversion of arachidonic acid (AA) into prostaglandin H2 (PGH2), being a precursor of physiologically active prostanoids [1]. It is generally recognized that PGHS-1 has two distinct catalytic activities: a cyclooxygenase (COX) activity converting AA to an intermediate product—prostaglandin G2 (PGG2)—and a peroxidase (POX) activity which further converts PGG2 into a final product—PGH2. PGHS-1 catalysis represents a complex network of many oxidized/reduced reactions connecting multiple enzyme intermediates and leading to redox transformation of key catalytic components such as the arachidonic acid (AA) binding site (COX site) and the heme-prosthetic group (POX site). Another not completely understood phenomenon in PGHS-1 catalysis is the so-called self-inactivation process, including gradual decay of both COX and POX activities during PGHS-1 catalysis [4].
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