Enzyme Activity Measurement for Nitric-Oxide Synthase (NADPH)

Creative Enzymes is an industrial biotech company specialized in enzyme activity assays. We partner with our diverse and unique customers to support them in their process optimization needs. True to our company’s tradition, we firmly believe that the quality of our work and our products is the basis of our corporate success. Here, Creative Enzymes is proud to offer the accurate catalytic assays for a wide range of enzymes, including nitric-oxide synthase (NADPH).

Nitric-oxide synthases (NADPH) (EC 1.14.13.39, L-arginine,NADPH:oxygen oxidoreductase (nitric-oxide-forming); NOS) are highly regulated proteins that catalyze the two-step oxidation of L-arginine to nitric oxide (NO) and citrulline via the stable intermediate nomega-hydroxy-L-arginine. In the first step, NOS hydroxylates L-arginine to nomega-hydroxy-L-arginine. In the second step, NOS oxidizes nomega-hydroxy-L-arginine to L-citrulline and NO. This cascade reaction is initiated by the two-electron donor NADPH in the reductase domain to the electron acceptor heme in the oxygenase domain through FAD and FMN with a series of proton transfers in the process. NOS can be found in various organisms, such as mammals, plants, and bacteria. In mammals, NOS has three different isoforms: 1) the inducible NOS (iNOS), which activates the immune system to destroy pathogens and microorganisms; 2) the endothelial NOS (eNOS), which regulates the relaxation of smooth muscle, resulting in a decrease of blood pressure; 3) the neuronal NOS (nNOS), which regulates the release of neurotransmitters and is related to the neuronal communication. All isoforms of the mammalian NOS are active only as homodimers. Each monomer consists of a C-terminal reductase domain harboring the binding sites for NADPH, FAD and FMN, and N-terminal oxygenase domain containing the binding sites for non-catalytic zinc (Zn²⁺), catalytic heme, essential cofactor H4B (tetrahydrobiopterin), and the substrate L-arginine.

Figure 1: Structure and catalytic mechanisms of functional NOS. (A) NOS monomers are capable of transferring electrons from NADPH to FAD and FMN. (B) In the presence of haem, NOS can form a functional dimer.
Reference: Förstermann, Ulrich et al. European Heart Journal. 2012, 33(7):829-837.

NO is an essential second messenger in mammals, which is involved in a variety of biological processes, such as vasodilation, smooth muscle relaxation, neurotransmission, and immune response. The biosynthesis of NO must be tightly regulated because uncontrolled NO production is associated with various pathological conditions, such as neurodegenerative diseases, arthritis, septic shock, and atherosclerosis. As a result, NOS serves as an important drug target for treating various disorders. More detailed knowledge of NOS should be gained to facilitate subsequent research of this enzyme in the medical and pharmaceutical industries. Although some research has been done to explore the molecular basis of its catalysis activity, the precise mechanism of complete NOS catalysis remains unclear. Creative Enzymes developed proper activity assays for the enzyme, based on deep understanding of its structure and properties with years of tests and exploration. Creative Enzymes is the leading company in the field of enzyme activity assay, and the highest standard for our product quality is the pillar of our global success and the basis of our best customer experience.

Figure 2: The crystal structure of human inducible nitric-oxide synthase.
PDB: 1NSI