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The binding constant is measured directly.\nexposure: Cyclic GMP binding to the isolated first GAF domain of phosphodiesterase type 5\nevidence_span: {\"source_cache\": \"artifacts/sildenafil-research/11032796.abstract.txt\", \"locator\": \"Indexed abstract; zero-based, end-exclusive Unicode character offsets\", \"file_sha256\": \"c3fde3e8ef99d45fbe9c59a9f4eba5a696b7e212dd2fc6d23999ce724d2996d9\", \"start_char\": 0, \"end_char\": 1012, \"text_sha256\": \"c3fde3e8ef99d45fbe9c59a9f4eba5a696b7e212dd2fc6d23999ce724d2996d9\"}\n[sil-p11032796] Structure of the GAF domain, a ubiquitous signaling motif and a new class of cyclic GMP receptor. 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