CLONING, AMINO-ACID-SEQUENCE AND TISSUE DISTRIBUTION OF PORCINE THIMET OLIGOPEPTIDASE - A COMPARISON WITH SOLUBLE ANGIOTENSIN-BINDING PROTEIN

We have previously determined the amino acid sequence of porcine soluble angiotensin-binding protein (sABP) by cDNA cloning and sequencing. In this study, we have cloned a sABP homologue (PABH) from the same porcine cDNA libraries used for sABP cloning. PABH and sABP have 65% sequence identity. Sequence comparisons with other proteins revealed very high similarities between porcine PABH and rat thimet oligopeptidase (90%), and between porcine sABP and rabbit microsomal endopeptidase (93%). This suggests that PABH and thimet oligopeptidase are identical and that sABP and microsomal endopeptidase are also the same. Indeed, sABP was shown to have a peptidase activity that is sensitive to the metal-chelating agents EDTA and 1,10-phenanthroline; sABP was also sensitive to the thiol reagent p-chloromercuriphenylsulfonic acid. RNase-protection assays, using RNA preparations from various porcine tissues, indicated that thimet oligopeptidase mRNA is ubiquitously expressed whereas sABP mRNA is predominantly expressed in the liver, kidney and adrenal gland. This assay also revealed tissue-specific alternative splicing of the sABP-encoding message.