Analysis of Angiotensin Metabolism in the Kidney Using Mass Spectrometry.

The renin angiotensin system (RAS) is a highly complex enzymatic system consisting of multiple peptide hormones, enzymes, and receptors. A thorough characterization of angiotensin peptide metabolism is crucial for understanding pathological states associated with an imbalanced RAS. Here, we describe two matrix-assisted laser desorption/ionization (MALDI) mass spectrometric (MS) approaches for the assessment of in vitro and in situ RAS enzymatic activities in the kidney using the natural angiotensin peptide substrates. These MS techniques demonstrate high specificity and are superior over conventional spectrophotometric or colorimetric assays since multiple proteolytic cleavage sites can be detected, thus unraveling the complexity of the RAS.