Which of the following enzyme degrades brain natriuretic peptide?
**Core Concept:** Brain natriuretic peptide (BNP) is a hormone produced by the ventricles of the heart in response to increased wall tension and volume overload. It plays a crucial role in regulating blood pressure, fluid balance, and cardiovascular homeostasis. The enzyme responsible for the degradation of BNP is called N-terminal pro-B-type natriuretic peptide (NT-proBNP).
**Why the Correct Answer is Right:** BNP is produced in response to increased wall tension and volume overload in the heart, acting as a stress hormone. It aids in reducing blood pressure, promoting diuresis, and natriuresis. NT-proBNP is an inactive precursor of BNP, which is cleaved into BNP by the enzyme called prohormone convertase 1/3 (PC1/3). This enzyme cleaves the prohormone, releasing active BNP and NT-proBNP.
**Why Each Wrong Option is Incorrect:**
A. Neutral endopeptidase (NEP) is an enzyme involved in the degradation of other peptides, such as atrial natriuretic peptide (ANP) and substance P. It is not responsible for degrading BNP.
B. Matrix Metallopeptidase-9 (MMP-9) is a protease enzyme involved in tissue remodeling and not specifically related to the degradation of BNP.
C. Angiotensin-converting enzyme (ACE) is responsible for converting angiotensin I to angiotensin II, which is a key enzyme in the renin-angiotensin-aldosterone system (RAAS). ACE does not degrade BNP.
D. Neutral endopeptidase (NEP) is involved in the degradation of other peptides like ANP and substance P, but not BNP.
**Clinical Pearl:** Monitoring the levels of NT-proBNP is a valuable diagnostic tool in clinical settings for evaluating heart failure, myocardial infarction, and other cardiovascular diseases, as it is a sensitive marker for cardiac stress and injury.