Nitric oxide synthase sequence homologies

In 1989, BH4 was found to be a cofactor for nitric oxide synthase (NOS) [ 126, 127]. BH4 is also involved in dimerization of NOS, as NOS is catalytically active in a homodimer structure. Three isoforms of NOS exist neuronal NOS (NOS 1), inducible NOS (NOS 2) and endothelial NOS (NOS 3). BH4 is essential for all NOS isoforms. The NOS isoforms share approximately 50-60% sequence homology. Each NOS polypeptide is comprised of oxygenase and reductase domains. An N-terminal oxygenase domain contains iron protoporphyrin IX (heme), BH4 and an arginine binding site, and a C-terminal reductase domain contains flavin mononucleotide (FMN), and a reduced nicotin-amide adenine dinucleotide phosphate (NADPH) binding site. 

PTPS (6-Pyruvoyl Tetmhydropterin Synthase). 6-Pyruvoyl tetrahy-dropterin synthase catalyzes formation of tetrahydrobiopterin biosynthesis. Tetrahydrobiopterin is a cofactor for several important enzymes, such as aromatic amino acid hydroxylases and nitric oxide synthase (57). H. pylori protein HPAG1 0913 shares homology with members of the protein domain family PTPS. H. pylori protein shares poor sequence identity of 14% with the PTPS profile at an E-value of 10 10 and covers about 95% of the length of the profile. Fold recognition results also confirm the relationship between H. pylori protein and the PTPS protein domain family. A fold recognition algorithm ensures fitness of the H. pylori protein sequence on the three-dimensional structure of PTPS from... 

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