Brain endo-oligopeptidase B: a post-proline cleaving enzyme that inactivates angiotensin I and II.

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Abstract
Rabbit brain endo-oligopeptidase B inactivates angiotensin I (Asp-Arg-Val-Tyr-Ile-His-Pro-Phe-His-Leu) and angiotensin II (Asp-Arg-Val-Tyr-Ile-His-Pro-Phe) by hydrolysis of the Pro7-Phe8 peptide bond. The site of hydrolysis was determined in preparative and analytical experiments in which both products were recovered in a molar ratio of 1:1, and the sum of the products plus unhydrolyzed substrate accounted for the starting material. The enzyme has a Km of 6.3 x 10(-5) M for angiotensin II at pH 8.3 and is activated 30-fold with 4.8 mM dithiothreitol. BPP9a ( less than Gln-Trp-Pro-Arg-Pro-Gln-Ile-Pro-Pro, SQ 20,881) inhibits the inactivation of angiotensin II with an I50 of 5 x 10(-5) M. BPP5a (less than Gln-Lys-Trp-Ala-Pro, SQ 20,475) is less active and D-3-mercapto-2-methylpropanoyl-L-proline (captopril, SQ 14,225) has essentially no activity. These endo-oligopeptidase B in angiotensin I and II metabolism remains to be established.