In the premier Episode 1 of Med School Question of the Week for USMLE, Leigh Finnegan examines the following: A 67-year-old man with a history of hypertension, type II diabetes, hyperlipidemia, and a myocardial infarction treated with coronary artery stenting presents to the emergency department with worsening dyspnea and orthopnea. On exam, his heart rate is 125 bpm, his respiratory rate is 31/breaths/minute, and his blood pressure is 106/65. On echocardiogram, his left ventricle is dilated and has an ejection fraction of 35%. As a result of the increased volume of fluid in the left ventricle, his heart releases a substance that promotes natriuresis, diuresis, and vasodilatation, and counteracts with myocardial fibrosis. Which of the following enzymes is responsible for degrading this substance?