Given an abstract from a research paper, your task is to identify and label relationships between chemical compounds and genes mentioned in the abstract.

The relationship type must be one of ['DOWNREGULATOR', 'SUBSTRATE', 'INDIRECT-REGULATOR', 'PART-OF', 'MODULATOR-ACTIVATOR', 'REGULATOR', 'INHIBITOR', 'COFACTOR', 'UPREGULATOR', 'ACTIVATOR', 'ANTAGONIST', 'NOT', 'INDIRECT-DOWNREGULATOR', 'SUBSTRATE_PRODUCT-OF', 'INDIRECT-UPREGULATOR', 'AGONIST', 'PRODUCT-OF', 'MODULATOR', 'DIRECT-REGULATOR', 'UNDEFINED', 'AGONIST-INHIBITOR', 'AGONIST-ACTIVATOR', 'MODULATOR-INHIBITOR'].

Please format your output as a JSON array. Each entry in the array should express a single relation, formatted as ["<Entity_A>", "<RELATION_A_B>", "<Entity_B>"]. If no relations can be found, please output an empty JSON array [].

Abstract:

A 46-amino acid segment in phosphodiesterase-5 GAF-B domain provides for high vardenafil potency over sildenafil and tadalafil and is involved in phosphodiesterase-5 dimerization. Phosphodiesterase-5 (PDE5) contains a catalytic domain (C domain) that hydrolyzes cGMP and a regulatory domain (R domain) that contains two mammalian cGMP-binding phosphodiesterase, Anabaena adenylyl cyclases, Escherichia coli FhlAs (GAFs) (A and B) and a phosphorylation site for cyclic nucleotide-dependent protein kinases (cNPKs). Binding of cGMP to GAF-A increases cNPK phosphorylation of PDE5 and improves catalytic site affinity for cGMP or inhibitors. GAF-B contributes to dimerization of PDE5, inhibition of cGMP binding to GAF-A, and sequestration of the phosphorylation site. To probe potential PDE5 R domain effects on catalytic site affinity for certain inhibitors, four N-terminal truncation mutants were generated: PDE5Delta1-321 contained GAF-B domain, C domain, and the sequence between GAF-A and -B; PDE5Delta1-419 contained GAF-B and C domain; PDE5Delta1-465 contained the C domain and the C-terminal portion of GAF-B; and PDE5Delta1-534 contained only C domain. Truncated proteins with a complete GAF-B were dimers, but those lacking the N-terminal 46 amino acids of GAF-B were monomers, indicating that these residues are vital for GAF-B-mediated PDE5 dimerization. K (m) values of the mutants for cGMP were similar to that of full-length PDE5. All PDE5 constructs had similar affinities for 3-isobutyl-1-methylxanthine, sildenafil, tadalafil, and UK-122764, but mutants containing a complete GAF-B had 7- to 18-fold higher affinity for vardenafil-based compounds compared with those lacking a complete GAF-B. This indicated that the N-terminal 46 amino acids in GAF-B are required for high vardenafil potency. This is the first evidence that PDE5 R domain, and GAF-B in particular, influences affinity and selectivity of the catalytic site for certain classes of inhibitors.
[["vardenafil", "REGULATOR", "GAF-B domain"], ["amino acids", "PART-OF", "GAF-B"], ["sildenafil", "REGULATOR", "phosphodiesterase-5"], ["cGMP", "INDIRECT-UPREGULATOR", "PDE5"], ["tadalafil", "DIRECT-REGULATOR", "GAF-B"], ["cGMP", "INDIRECT-UPREGULATOR", "cNPK"], ["UK-122764", "DIRECT-REGULATOR", "PDE5"], ["vardenafil", "REGULATOR", "phosphodiesterase-5"], ["3-isobutyl-1-methylxanthine", "DIRECT-REGULATOR", "GAF-B"], ["sildenafil", "DIRECT-REGULATOR", "PDE5"], ["cGMP", "DIRECT-REGULATOR", "PDE5"], ["tadalafil", "DIRECT-REGULATOR", "PDE5"], ["cGMP", "SUBSTRATE", "PDE5"], ["sildenafil", "REGULATOR", "GAF-B domain"], ["tadalafil", "REGULATOR", "phosphodiesterase-5"], ["3-isobutyl-1-methylxanthine", "DIRECT-REGULATOR", "PDE5"], ["UK-122764", "DIRECT-REGULATOR", "GAF-B"], ["cGMP", "SUBSTRATE", "Phosphodiesterase-5"], ["sildenafil", "DIRECT-REGULATOR", "GAF-B"], ["tadalafil", "REGULATOR", "GAF-B domain"], ["cGMP", "DIRECT-REGULATOR", "GAF-A"], ["vardenafil", "REGULATOR", "GAF-B"]]