Characterization of immunoreactive acetyl-Ser-Asp-Lys-Pro in human plasma and urine by liquid chromatography-electrospray mass spectrometry

The tetrapeptide AcSDKP, a natural and specific substrate of angiotensin I- converting enzyme (ACE), is a negative regulator of hematopoiesis. AcSDKP h as been measured in various biological media using an enzyme immunoassay (E IA), but its presence in human plasma and urine has not been formally estab lished. By using immunoaffinity extraction and liquid chromatography-electr ospray mass spectrometry, we demonstrate that AcSDKP-like immunoreactivity measured with EIA in plasma and urine samples from untreated, captopril- (a n ACE inhibitor) and AcSDKP-treated subjects corresponds to AcSDKP. The pre sent study confirms that AcSDKP is naturally present in human plasma and ur ine and that EIA is reliable for its measurement in such media. (C) 2001 El sevier Science BN. All rights reserved.