Found in humans: 3.1.4.17, 4.6.1.1., 4.6.1.2. According to BRENDA, 3.1.4.35 is also found in humans. UniProt Protein PDE5A_HUMAN Tissue specificity: Expressed in aortic smooth muscle cells, heart, placenta, skeletal muscle and pancreas and, to a much lesser extent, in brain, liver and lung.